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Practice › LeetCode › LeetCode 34xx ›

LeetCode 3421 - Find Students Who Improved

LeetCode Problem 3421 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This This ensures that performance in one subject never affects another subject's result.

Practice › LeetCode › LeetCode 36xx ›

LeetCode 3601 - Find Drivers with Improved Fuel Efficiency

LeetCode Problem 3601 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks final stage, preserving accuracy during computation and preventing premature rounding errors from affecting averages or comparisons.

Practice › LeetCode › LeetCode 36xx ›

LeetCode 3611 - Find Overbooked Employees

LeetCode Problem 3611 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 3611 - Find Overbooked Employees Problem Understanding This problem asks us to identify employees who spend an excessive amount of their working time in meetings. We are given two tables: The employees table contains employee information, including their unique identifier, name, and department. The meetings table contains meeting attendance records. Each record tells us which employee attended a meeting, on...

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3564 - Seasonal Sales Analysis

LeetCode Problem 3564 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The task asks us to determine the most popular product category for each season based on sales data. We are given two tables: a sales table containing individual transaction records and a products table that maps each product to its category. The goal is to aggregate sales at the category level within each season and then select the top...

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3521 - Find Product Recommendation Pairs

LeetCode Problem 3521 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to identify product pairs that are frequently purchased by the same customers. The goal is to support a recommendation feature similar to "Customers who bought this also bought...", where products that commonly appear together in customer purchase histories can be suggested to future buyers. The ProductPurchases table contains one row for each (user_id, product_id) combination....

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3482 - Analyze Organization Hierarchy

LeetCode Problem 3482 Difficulty: 🔴 Hard Topics: Database Solution LeetCode 3482 - Analyze Organization Hierarchy Problem Understanding This problem is a hierarchical organization analysis task over an employee table that forms a tree structure. Each employee has a unique employee_id , a name, a salary, and a manager_id . The employee whose manager_id is NULL is the CEO and serves as the root of the organization tree. Every other employee...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3401 - Find Circular Gift Exchange Chains

LeetCode Problem 3401 Difficulty: 🔴 Hard Topics: Database Solution Here’s a full technical solution guide following your requested format for LeetCode 3401 - Find Circular Gift Exchange Chains : Problem Understanding This problem asks us to analyze a table of gift exchanges in a Secret Santa setting and identify circular chains of gift exchanges. Each row in the SecretSanta table represents a gift transaction, with giver_id as the person giving...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3415 - Find Products with Three Consecutive Digits

LeetCode Problem 3415 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This is a SQL database problem involving pattern matching on strings. We are given a table named Products with two columns: Column Description product_id Unique identifier for each product name Product name string The goal is to return all products whose names contain a sequence of exactly three consecutive digits . The important detail is the word exactly ....

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3586 - Find COVID Recovery Patients

LeetCode Problem 3586 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The task is to identify patients who have recovered from COVID based on their testing history. We are given two tables: one containing patient demographic information and another containing COVID test records with timestamps and results. A patient is considered recovered if they have at least one positive test and, after that positive test, they later have at least...

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3580 - Find Consistently Improving Employees

LeetCode Problem 3580 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The task asks us to identify employees whose performance has consistently improved over their most recent three performance reviews. Each employee may have multiple reviews stored in the performance_reviews table, and we must focus only on the last three reviews per employee when ordered by review_date . For each employee, we first determine whether they have at least three...

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3570 - Find Books with No Available Copies

LeetCode Problem 3570 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify books in a library system that are both fully unavailable for borrowing and currently have active borrowers who have not returned them yet. We are given two tables. The library_books table contains static information about each book, including how many total physical copies exist in the library. The borrowing_records table captures individual borrow...

Practice › LeetCode › LeetCode 35xx ›

LeetCode 3554 - Find Category Recommendation Pairs

LeetCode Problem 3554 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This is a SQL database problem involving customer purchasing behavior across product categories. We are given two tables: ProductPurchases records which products each user purchased. A user may purchase multiple products, and each purchase has a quantity. The quantity is irrelevant for this problem because we only care whether a user bought from a category, not how much they...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3497 - Analyze Subscription Conversion

LeetCode Problem 3497 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This is a SQL aggregation problem where we need to analyze user subscription behavior and return statistics only for users who successfully converted from a free trial to a paid subscription. The UserActivity table contains one row per user, per day, per activity type. The activity_type column can be one of three values: This is a SQL database problem...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3475 - DNA Pattern Recognition

LeetCode Problem 3475 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 3475 - DNA Pattern Recognition Problem Understanding This problem provides a database table named Samples that contains DNA sequences and their associated species. Each row represents a single biological sample, identified by a unique sample_id . The task is to examine every DNA sequence and determine whether it matches four different biological patterns. For each sample, we must generate four...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3465 - Find Products with Valid Serial Numbers

LeetCode Problem 3465 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to query a database table called products to identify rows where the description column contains a valid serial number. A valid serial number is defined as a substring that begins with "SN", followed by exactly four digits, a hyphen, and then exactly four more digits. For example, SN1234-5678 is valid, but SN123-4567 or SN12345-6789 are...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3451 - Find Invalid IP Addresses

LeetCode Problem 3451 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This is a SQL database problem where we must identify all invalid IPv4 addresses that appear in the logs table and count how many times each invalid address occurs. The input table contains one row per server access log. Each row includes a unique log_id , an IP address stored as a string in the ip column, and an...

Practice › LeetCode › LeetCode 34xx ›

LeetCode 3436 - Find Valid Emails

LeetCode Problem 3436 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires us to identify valid email addresses from a Users table in a database. Each row contains a user_id and an email string. The definition of a valid email is very specific: it must contain exactly one @ symbol , end with .com , have a local part (before the @ ) composed solely of alphanumeric characters...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3390 - Longest Team Pass Streak

LeetCode Problem 3390 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to analyze a football match pass sequence and determine, for every team, the longest uninterrupted sequence of successful passes between players on the same team. We are given two tables: The Teams table maps each player_id to a team_name . Every player belongs to exactly one team. The Passes table records passes made during the...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3188 - Find Top Scoring Students II

LeetCode Problem 3188 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to identify students who satisfy a combination of academic requirements based on their major, completed courses, grades, and overall GPA. We are given three tables: The students table stores each student's identity and declared major. The courses table stores information about courses, including which major they belong to and whether they are mandatory or elective....

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1867 - Orders With Maximum Quantity Above Average

LeetCode Problem 1867 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to identify "imbalanced orders" from an OrdersDetails table. Each row represents a product within an order, containing the order_id , product_id , and quantity ordered. An order can have multiple products, meaning multiple rows can share the same order_id . An imbalanced order is defined as one whose maximum quantity of any single product is...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2377 - Sort the Olympic Table

LeetCode Problem 2377 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to return the rows of the Olympic table in a very specific sorted order. Each row represents a country and the number of gold, silver, and bronze medals that country won in the Olympic games. The table contains four columns: country , the country name gold_medals , the number of gold medals silver_medals , the...

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2837 - Total Traveled Distance

LeetCode Problem 2837 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires calculating the total distance traveled by each user based on ride data stored in a relational database. We are given two tables: Users and Rides . The Users table contains user_id and name , where user_id is unique. The Rides table contains ride_id , user_id , and distance , where ride_id is unique. Each row in...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3236 - CEO Subordinate Hierarchy

LeetCode Problem 3236 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem requires building a hierarchical view of a company's employee structure starting from the CEO. The Employees table contains employee records, including their unique ID, name, manager ID, and salary. The CEO is identified as the employee with a NULL manager_id . The task is to return all subordinates of the CEO, both direct and indirect , along...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3246 - Premier League Table Ranking

LeetCode Problem 3246 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 3246 - Premier League Table Ranking Problem Understanding This problem asks us to generate a league standings table from a database table named TeamStats . Each row in the table represents a football team and stores how many matches the team has played, won, drawn, and lost. The main task is to compute two derived values for every team: points...

Practice › LeetCode › LeetCode 25xx ›

LeetCode 2504 - Concatenate the Name and the Profession

LeetCode Problem 2504 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to transform data in a SQL table named Person . Each row represents a person, with three columns: person_id , name , and profession . The profession column is an ENUM containing one of six possible values: 'Doctor' , 'Singer' , 'Actor' , 'Player' , 'Engineer' , or 'Lawyer' . The task is to return...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2112 - The Airport With the Most Traffic

LeetCode Problem 2112 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to find the airport(s) with the most traffic using a table of flights. Each row of the Flights table represents a direct connection from departure_airport to arrival_airport along with the number of flights flights_count for that route. The traffic for an airport is defined as the total number of flights departing from or arriving at...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2173 - Longest Winning Streak

LeetCode Problem 2173 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem is asking us to determine the longest sequence of consecutive wins, also called a winning streak, for each player in a match history. The input is a Matches table with three columns: player_id , match_day , and result . Each row represents one match played by a specific player on a given day, with the match result...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2687 - Bikes Last Time Used

LeetCode Problem 2687 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires us to identify the last time each bike was used based on a table of rides. Each row of the table corresponds to a unique ride and contains the ride_id , bike_number , start_time , and end_time . Our task is to produce a result showing the latest end_time for each bike. Additionally, the results must...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2994 - Friday Purchases II

LeetCode Problem 2994 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem requires calculating the total spending by users on each Friday in November 2023 , broken down by week of the month . The input is a Purchases table containing user_id , purchase_date , and amount_spend . The output must include all Fridays in November, and for any Friday with no purchases, the total should be reported as...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2199 - Finding the Topic of Each Post

LeetCode Problem 2199 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem gives us two database tables, Keywords and Posts . The Keywords table maps words to topic IDs. A single topic can have multiple words associated with it, and a single word may belong to multiple topics. For example, the word "football" might represent topic 1 , while another word such as "war" might represent topic 3 ....

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2082 - The Number of Rich Customers

LeetCode Problem 2082 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Store . Each row in the table represents a single bill issued to a customer. The table contains three columns: bill_id , which uniquely identifies a bill customer_id , which identifies the customer associated with the bill amount , which stores the bill amount We need to determine how many distinct...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2298 - Tasks Count in the Weekend

LeetCode Problem 2298 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem provides a database table named Tasks , where each row represents a submitted task. Every task contains three fields: task_id , the unique identifier for the task assignee_id , the user assigned to the task submit_date , the date the task was submitted The goal is to compute two aggregated counts: weekend_cnt , the number of tasks...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2922 - Market Analysis III

LeetCode Problem 2922 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to analyze three relational tables: Users , Items , and Orders . Each user (seller) has a favorite brand, each item has a brand, and orders record which seller sold which item on which date. We are asked to determine the top seller(s) based on the number of unique items sold that have a different...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2978 - Symmetric Coordinates

LeetCode Problem 2978 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to identify symmetric coordinate pairs from a database table called Coordinates . Each row in the table represents a coordinate (X, Y) , and duplicate rows are allowed. Two coordinates are considered symmetric if they satisfy the following condition: (X1, Y1) and (X2, Y2) are symmetric when X1 == Y2 and X2 == Y1 In...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2329 - Product Sales Analysis V

LeetCode Problem 2329 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to calculate how much money each user has spent across all of their purchases. We are given two database tables: The Sales table stores purchase records. Each row represents a transaction involving a specific product bought by a user, along with the quantity purchased. The Product table stores the price of each product. To compute...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2175 - The Change in Global Rankings

LeetCode Problem 2175 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to determine how the global rankings of national teams change after their points are updated. We are given two database tables: The TeamPoints table contains the current ranking information for each team. Every row includes: team_id , the unique identifier for the team name , the country name points , the current ranking points The...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2159 - Order Two Columns Independently

LeetCode Problem 2159 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem provides a database table named Data with two integer columns: first_col and second_col . Each row represents a pair of numbers, and duplicate rows are allowed. The task is to return a new table where the numbers in each column are independently sorted: first_col in ascending order and second_col in descending order. Importantly, the sorting of one...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2324 - Product Sales Analysis IV

LeetCode Problem 2324 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to analyze sales data to determine which products each user spent the most money on. We are given two tables: Sales and Product . The Sales table contains individual transactions, showing which user bought which product and in what quantity. The Product table contains the price of each product. The task is to calculate the...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3087 - Find Trending Hashtags

LeetCode Problem 3087 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to find the top 3 trending hashtags from a table of tweets for a specific month, February 2024. Each tweet contains exactly one hashtag. The input is represented by a Tweets table with columns user_id , tweet_id , tweet , and tweet_date . The tweet_id is unique for each row, and tweet contains a string...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3308 - Find Top Performing Driver

LeetCode Problem 3308 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to identify the top-performing driver for each fuel type based on the trips data. We are given three tables: Drivers , Vehicles , and Trips . Each driver may operate one or more vehicles, and each vehicle may have multiple trips. The goal is to compute, for each fuel type, the driver with the highest...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2480 - Form a Chemical Bond

LeetCode Problem 2480 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to identify all valid chemical bonds that can form between elements in a given table. The Elements table contains three columns: symbol , type , and electrons . The type column is an enumeration of 'Metal' , 'Nonmetal' , and 'Noble' . The electrons column indicates how many electrons a metal can give or a...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3103 - Find Trending Hashtags II

LeetCode Problem 3103 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem gives us a database table named Tweets , where each row represents a tweet posted during February 2024. Every tweet contains plain text in the tweet column, and that text may contain one or more hashtags. A hashtag is a word that starts with the # character, such as #HappyDay or #TechLife . Our task is to...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1907 - Count Salary Categories

LeetCode Problem 1907 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to classify bank accounts into three salary categories based on their monthly income, then count how many accounts belong to each category. The input is a database table named Accounts . Each row contains two columns: account_id , which uniquely identifies a bank account income , which represents the monthly income associated with that account...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3252 - Premier League Table Ranking II

LeetCode Problem 3252 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to compute a Premier League-style ranking table from a TeamStats table, which contains each team's matches played, wins, draws, and losses. We are required to calculate three additional columns for each team: points , position , and tier . Points are calculated with the standard football scoring system: 3 points per win, 1 point per...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1972 - First and Last Call On the Same Day

LeetCode Problem 1972 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem provides a table of phone call records where each row contains a caller, a recipient, and a timestamp. Each call is bidirectional in the sense that both participants are considered to have made and received the call simultaneously. The goal is to identify all users who, on at least one calendar day, had their first call and...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2986 - Find Third Transaction

LeetCode Problem 2986 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us a Transactions table that stores three pieces of information for every transaction: user_id , which identifies the user spend , which represents the transaction amount transaction_date , which represents when the transaction occurred The pair (user_id, transaction_date) is guaranteed to be unique, which means a user cannot have two transactions at the exact same timestamp....

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3220 - Odd and Even Transactions

LeetCode Problem 3220 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem provides a database table named transactions , where each row represents a transaction with three fields: transaction_id , a unique identifier amount , the transaction amount transaction_date , the date on which the transaction occurred For every distinct transaction_date , we need to compute two separate sums: odd_sum , the total amount of all transactions whose amount...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2688 - Find Active Users

LeetCode Problem 2688 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us a database table named Users . Each row represents a purchase made by a user. The columns include: user_id , the identifier of the user item , the purchased product created_at , the purchase timestamp amount , the purchase value The table may contain duplicate rows, which means we cannot assume uniqueness of purchases. We...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3293 - Calculate Product Final Price

LeetCode Problem 3293 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to calculate the final price for each product in a database, taking into account any category-specific discounts. We are given two tables: Products and Discounts . The Products table contains each product's unique ID, its category, and its original price. The Discounts table contains a discount percentage for each category. Our goal is to produce...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3268 - Find Overlapping Shifts II

LeetCode Problem 3268 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to analyze shift overlaps for employees. We are given a table EmployeeShifts with columns employee_id , start_time , and end_time . Each row represents one work shift for an employee. Two shifts are considered overlapping if they occur on the same date and the end_time of one shift is later than the start_time of another...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2072 - The Winner University

LeetCode Problem 2072 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us two database tables, NewYork and California . Each table contains the exam scores of students from a university. Every row represents a single student, identified by a unique student_id , along with their score . The competition rule is straightforward. A student is considered an excellent student if their score is greater than or equal...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2362 - Generate the Invoice

LeetCode Problem 2362 Difficulty: 🔴 Hard Topics: Database Solution LeetCode 2362 - Generate the Invoice Problem Understanding This is a SQL database problem involving two tables: Products product_id price Unique product identifier Unit price of the product Purchases invoice_id product_id quantity Invoice identifier Product purchased Number of units purchased Each row in Purchases represents one product included in an invoice. Since (invoice_id, product_id) is the primary key, the same product...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2252 - Dynamic Pivoting of a Table

LeetCode Problem 2252 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem requires implementing a SQL-style pivot operation programmatically. The input is a table named Products with columns product_id , store , and price , where each row represents the price of a product in a specific store. The table has a compound primary key (product_id, store) and at most 30 unique stores. The goal is to reorganize the...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2669 - Count Artist Occurrences On Spotify Ranking List

LeetCode Problem 2669 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named Spotify that contains information about songs appearing in a Spotify ranking list. Each row represents one ranked track and contains three columns: id , a unique identifier for the row track_name , the name of the song artist , the name of the artist who performed the track The task is to...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2346 - Compute the Rank as a Percentage

LeetCode Problem 2346 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem provides a database table named Students , where each row represents a student and contains three fields: student_id , the unique identifier for the student department_id , the department the student belongs to mark , the student's exam score The goal is to compute each student's rank percentage inside their department. The ranking is based on descending...

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2853 - Highest Salaries Difference

LeetCode Problem 2853 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Salaries with three columns: Column Meaning emp_name Employee name department Employee department salary Employee salary The combination of (emp_name, department) is unique, meaning there are no duplicate employee entries within the same department. The task is to compute the absolute difference between: The highest salary in the Engineering department The highest salary...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2738 - Count Occurrences in Text

LeetCode Problem 2738 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to analyze a database table named Files that contains two columns: file_name and content . Each row corresponds to a unique file and its textual content. The task is to count the number of files that contain the words "bull" and "bear" as standalone words, meaning the words must be separated by spaces, punctuation, or...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3051 - Find Candidates for Data Scientist Position

LeetCode Problem 3051 Difficulty: 🟢 Easy Topics: Database Solution You included two different LeetCode problems with conflicting templates. The second problem appears to be the one you want covered: LeetCode 3051 - Find Candidates for Data Scientist Position (Database) However, the required sections still reference Python and Go solutions, test cases with assert , and algorithm walkthroughs, which do not apply to a SQL database problem. For a Database problem,...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3358 - Books with NULL Ratings

LeetCode Problem 3358 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named books . Each row in the table represents a single book and contains information such as the book's ID, title, author, publication year, and rating. The important detail is that the rating column can contain NULL values. In SQL, NULL represents the absence of a value, meaning the book has not been...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2984 - Find Peak Calling Hours for Each City

LeetCode Problem 2984 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem is asking us to analyze call records from a Calls table and determine the peak calling hour for each city. Each row in the table contains a caller_id , recipient_id , a timestamp ( call_time ), and the city where the call originated. The goal is to find which hour(s) of the day (0-23) saw the maximum...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2991 - Top Three Wineries

LeetCode Problem 2991 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to determine the top three wineries in each country based on the total points accumulated by each winery. We are given a table called Wineries that contains columns id , country , points , and winery . Each row represents a wine evaluation from a specific winery in a given country. Our task is to...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1892 - Page Recommendations II

LeetCode Problem 1892 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to implement a page recommendation system based on users’ friendships and their page likes. We are given two database tables: Friendship and Likes . The Friendship table contains pairs of users who are friends, and the Likes table contains pairs of users and pages that they have liked. The goal is to recommend pages to...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3328 - Find Cities in Each State II

LeetCode Problem 3328 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us a database table named cities , where each row contains a state name and a city name. The pair (state, city) is guaranteed to be unique, which means the same city will not appear twice for the same state. We must generate a report for qualifying states. A state qualifies only if it satisfies two...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3057 - Employees Project Allocation

LeetCode Problem 3057 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to identify employees whose assigned project workload is greater than the average workload of employees within their own team. We are given two database tables: The Project table stores information about project assignments. Each row tells us: which project an employee is working on, which employee is assigned, and the workload value associated with that...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2989 - Class Performance

LeetCode Problem 2989 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to calculate the difference between the highest and lowest total scores among students in a class. Each student has three assignment scores, and the total score is simply the sum of these three values. The input is a database table named Scores with columns student_id , student_name , assignment1 , assignment2 , and assignment3 ....

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2474 - Customers With Strictly Increasing Purchases

LeetCode Problem 2474 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem gives us an Orders table where each row represents a purchase made by a customer. Every order has an order_id , a customer_id , an order_date , and a price . We need to find all customers whose yearly total purchases are strictly increasing from their first purchase year to their last purchase year. The key detail...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2118 - Build the Equation

LeetCode Problem 2118 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to construct a polynomial equation from a database table called Terms . Each row in the table represents a single term in the equation, where power is the exponent of X and factor is the coefficient. The goal is to output a single string representing the equation, where all terms are concatenated in descending order...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2990 - Loan Types

LeetCode Problem 2990 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires identifying users who have taken both a "Refinance" loan and a "Mortgage" loan. The input is a table Loans containing loan_id , user_id , and loan_type . Each row represents one loan taken by a user, and loan_id is unique. We are asked to return a list of distinct user_id values who satisfy the condition of...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1990 - Count the Number of Experiments

LeetCode Problem 1990 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem gives us a database table named Experiments . Each row represents a single experiment performed by a participant. Every experiment belongs to one platform and one experiment category. The table contains three columns: Column Meaning experiment_id Unique identifier for the experiment platform One of Android , IOS , or Web experiment_name One of Reading , Sports ,...

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LeetCode 3374 - First Letter Capitalization II

LeetCode Problem 3374 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to transform text stored in a database table while preserving the original formatting structure. The table user_content contains two columns: a unique content_id and a content_text string. For every row, we must generate a new version of the text where each word follows title case formatting rules. More specifically, every word must be converted so...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2314 - The First Day of the Maximum Recorded Degree in Each City

LeetCode Problem 2314 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us a database table named Weather that stores temperature readings for different cities on specific days in the year 2022. Each row contains three values: city_id , which identifies the city day , which represents the date of the measurement degree , which represents the recorded temperature The pair (city_id, day) is guaranteed to be unique,...

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LeetCode 3126 - Server Utilization Time

LeetCode Problem 3126 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem provides a table named Servers that records status changes for multiple servers over time. Each row contains three values: server_id , which identifies the server status_time , which indicates when the status change occurred session_status , which is either 'start' or 'stop' A 'start' row means the server began running at that timestamp, while a 'stop' row...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2686 - Immediate Food Delivery III

LeetCode Problem 2686 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to calculate the percentage of immediate food delivery orders for each unique order_date . The Delivery table contains one row per order. Each row includes: delivery_id : A unique identifier for the delivery. customer_id : The customer who placed the order. order_date : The date when the order was placed. customer_pref_delivery_date : The date the...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1853 - Convert Date Format

LeetCode Problem 1853 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Days with a single column called day . Each value in this column is a valid SQL DATE , and every value is unique. The task is to transform each date into a human readable string format: "day_name, month_name day, year" For example: 2022-04-12 should become: Tuesday, April 12, 2022 The output...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2701 - Consecutive Transactions with Increasing Amounts

LeetCode Problem 2701 Difficulty: 🔴 Hard Topics: Database Solution Before I generate it, there is one important issue to resolve: LeetCode 2701 is a SQL-only Database problem , so there is no valid Python or Go LeetCode-submittable solution signature for this problem. If I strictly follow your requested template, the Python and Go sections would have to be artificial simulations rather than actual LeetCode submissions. I can proceed in one...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1919 - Leetcodify Similar Friends

LeetCode Problem 1919 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem involves analyzing two database tables, Listens and Friendship , to determine pairs of "similar friends." In plain terms, we are asked to find pairs of users who are friends and who listened to at least three different songs on the same day . The Listens table contains the listening history of users, with each row representing a...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2356 - Number of Unique Subjects Taught by Each Teacher

LeetCode Problem 2356 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires calculating the number of unique subjects each teacher teaches in a university, given a table that maps teachers to subjects and departments. Each row in the Teacher table represents a specific combination of a teacher, a subject, and a department. A teacher may teach the same subject in multiple departments, but for this problem, we only...

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LeetCode 2720 - Popularity Percentage

LeetCode Problem 2720 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The Friends table stores friendship relationships between users on a social platform. Each row contains two user IDs, user1 and user2 , indicating that those two users are friends with each other. The task is to compute a popularity percentage for every user who appears anywhere in the table. The popularity percentage is defined as: $\text{Popularity Percentage} = \frac{\text{Number...

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2854 - Rolling Average Steps

LeetCode Problem 2854 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 2854 - Rolling Average Steps Problem Understanding This problem asks us to compute a 3-day rolling average of daily step counts for each user. The input is a table named Steps , where each row contains: user_id , identifying a user. steps_count , the number of steps taken on a particular day. steps_date , the date associated with that step...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3182 - Find Top Scoring Students

LeetCode Problem 3182 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us three relational database tables: students , which stores each student's ID, name, and major courses , which stores all courses along with the major they belong to enrollments , which stores which students took which courses and the grade they received We must return the IDs of students who satisfy two conditions simultaneously: They have...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2205 - The Number of Users That Are Eligible for Discount

LeetCode Problem 2205 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a table named Purchases , where each row represents a purchase made by a user. Every record contains three fields: user_id , identifying the customer time_stamp , indicating when the purchase happened amount , representing how much money was spent The pair (user_id, time_stamp) is unique, which means the same user cannot have two purchases...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1934 - Confirmation Rate

LeetCode Problem 1934 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to calculate the confirmation rate for each user in a system where users can request confirmation messages after signing up. We are given two tables: Signups and Confirmations . The Signups table contains all users who signed up, with a unique user_id and a time_stamp of signup. The Confirmations table contains records of each confirmation...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3166 - Calculate Parking Fees and Duration

LeetCode Problem 3166 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to analyze parking transaction records and compute aggregated statistics for each car. Every row in the ParkingTransactions table represents one parking session, containing the parking lot ID, the car ID, the entry and exit timestamps, and the fee paid for that session. For every distinct car_id , we must compute three values: The total parking...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3384 - Team Dominance by Pass Success

LeetCode Problem 3384 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to compute a dominance score for each football team across two halves of a match, based on passing outcomes. The input is represented using two database tables, Teams and Passes . The Teams table maps every player to exactly one team. Since player_id is unique, each player belongs to only one team for the duration...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2066 - Account Balance

LeetCode Problem 2066 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to compute the running balance for every bank account after each transaction. We are given a table named Transactions where each row represents a single transaction performed by an account on a particular day. Every transaction has: Column Meaning account_id The account performing the transaction day The date of the transaction type Either Deposit or...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3060 - User Activities within Time Bounds

LeetCode Problem 3060 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The Sessions table stores information about user activity sessions on a platform. Each row represents a single session and contains: Column Meaning user_id The user who performed the session session_start When the session began session_end When the session ended session_id Unique identifier for the session session_type Either Viewer or Streamer The problem asks us to find every user who...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2752 - Customers with Maximum Number of Transactions on Consecutive Days

LeetCode Problem 2752 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem gives us a database table named Transactions . Each row represents a transaction made by a customer on a specific date. The important detail is that the pair (customer_id, transaction_date) is guaranteed to be unique, which means a customer can make at most one transaction per day. We need to determine which customers achieved the maximum number...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1917 - Leetcodify Friends Recommendations

LeetCode Problem 1917 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem requires generating friend recommendations for users on the Leetcodify platform based on their listening habits. We are given two tables: Listens and Friendship . The Listens table logs when a user listens to a particular song on a specific day, and it may contain duplicates. The Friendship table lists all pairs of users who are already friends....

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2339 - All the Matches of the League

LeetCode Problem 2339 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The Teams table contains the names of all teams participating in a league. Each row represents exactly one team, and the team_name column is guaranteed to contain unique values. The problem asks us to generate every possible match in the league under the following rule: Every pair of teams plays twice. In one match, Team A is the home...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2292 - Products With Three or More Orders in Two Consecutive Years

LeetCode Problem 2292 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem provides a table named Orders , where each row represents a single purchase event. Every order contains an order_id , a product_id , the purchased quantity , and the purchase_date . The goal is to identify all products that satisfy two conditions simultaneously: The product was ordered at least three times in one year. The same product...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3150 - Invalid Tweets II

LeetCode Problem 3150 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Tweets with two columns: Column Description tweet_id Unique identifier for each tweet content The text content of the tweet We need to identify all tweets that are considered invalid. A tweet becomes invalid if at least one of the following conditions is true: The tweet content length is greater than 140...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2253 - Dynamic Unpivoting of a Table

LeetCode Problem 2253 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to transform a wide table into a normalized row-based format. The database table Products contains one row per product, and each store has its own dedicated column. The value inside a store column represents the product's price in that store. For example, a row might look like this: product_id LC_Store Nozama Shop 1 100 null...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2668 - Find Latest Salaries

LeetCode Problem 2668 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 2668 - Find Latest Salaries Problem Understanding This problem gives us a database table named Salary that stores employee salary records. Each employee may appear multiple times because older salary records are still kept in the table. The key observation is that salaries are guaranteed to increase every year, which means the largest salary value for an employee must represent...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3278 - Find Candidates for Data Scientist Position II

LeetCode Problem 3278 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 3278 - Find Candidates for Data Scientist Position II Problem Understanding This problem asks us to determine the best candidate for every project based on required skills and a scoring system. We are given two database tables. The Candidates table stores information about each candidate's skills and proficiency levels. Each row represents one skill for one candidate. A candidate may...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1890 - The Latest Login in 2020

LeetCode Problem 1890 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table Logins that records user login events, with columns user_id and time_stamp . Each combination of (user_id, time_stamp) is unique, ensuring that every row corresponds to a distinct login. The task is to determine, for each user who logged in at least once during the year 2020, the latest login timestamp in that year...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1951 - All the Pairs With the Maximum Number of Common Followers

LeetCode Problem 1951 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem provides a relational table named Relations , where each row indicates a directed following relationship: a user identified by follower_id follows another user identified by user_id . In other words, each user_id has a set of followers, and the same follower can follow multiple users. The task is to find all pairs of distinct users (user1_id, user2_id)...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1978 - Employees Whose Manager Left the Company

LeetCode Problem 1978 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to find employees in a company who meet two specific conditions. First, their salary must be strictly less than $30,000. Second, their manager has left the company, meaning there is no corresponding row for the manager in the Employees table even though the manager_id field in the employee's record still references that manager. The...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2230 - The Users That Are Eligible for Discount

LeetCode Problem 2230 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify all users who qualify for a discount based on their purchase history stored in the Purchases table. Each row in the table contains three pieces of information: user_id , the identifier of the user time_stamp , the exact date and time when a purchase occurred amount , the amount paid during that purchase...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3204 - Bitwise User Permissions Analysis

LeetCode Problem 3204 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem is asking us to analyze a table of user permissions where each user's permissions are encoded as an integer. Each bit in this integer represents a distinct access level or feature. The goal is to compute two aggregate permission values: common_perms , which represents the set of permissions that every user has, and any_perms , which represents...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2228 - Users With Two Purchases Within Seven Days

LeetCode Problem 2228 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem requires identifying users who made at least two purchases within a 7-day window. We are given a Purchases table with purchase_id , user_id , and purchase_date . Each row represents a single purchase made by a user. The goal is to return the IDs of users who had two or more purchases where the difference between any...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1939 - Users That Actively Request Confirmation Messages

LeetCode Problem 1939 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify users who requested confirmation messages at least twice within a 24 hour time window. We are given two database tables: The Signups table contains one row per user and records when the user signed up. The user_id column is unique. The Confirmations table contains confirmation message requests. Every row represents a confirmation request...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1988 - Find Cutoff Score for Each School

LeetCode Problem 1988 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to compute a minimum score requirement (cutoff score) for each school such that the number of students who meet or exceed that score does not exceed the school’s capacity, while also making that number as large as possible. The Exam table does not list individual students but instead gives aggregated data: for each score threshold,...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3061 - Calculate Trapping Rain Water

LeetCode Problem 3061 Difficulty: 🔴 Hard Topics: Database Solution LeetCode 3061 - Calculate Trapping Rain Water Problem Understanding This problem asks us to compute how much rainwater can be trapped between vertical bars after rainfall. The bars are represented in a database table named Heights , where each row contains an id and a height . The id values are sequential, which means they define the left-to-right order of the...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3172 - Second Day Verification

LeetCode Problem 3172 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires identifying users who verified their signup exactly on the second day after registering. We have two tables: emails and texts . The emails table contains the email_id , the user_id , and the signup_date . The texts table records actions taken by emails, including whether they were verified, along with the action_date . The task is...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2142 - The Number of Passengers in Each Bus I

LeetCode Problem 2142 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem involves simulating passengers arriving at a bus station and boarding buses as they arrive. We are given two tables: Buses and Passengers . Each bus has a unique bus_id and an arrival_time , and each passenger has a unique passenger_id and an arrival_time . Passengers board the first bus that arrives after their arrival time, and each...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3156 - Employee Task Duration and Concurrent Tasks

LeetCode Problem 3156 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem gives us a table named Tasks , where each row represents a task assigned to an employee. Every task has a start timestamp and an end timestamp. Multiple tasks may overlap in time for the same employee. We need to compute two values for every employee: The total amount of time the employee spent working on tasks....

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3050 - Pizza Toppings Cost Analysis

LeetCode Problem 3050 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to compute the total cost of all possible three-topping pizza combinations using a list of available toppings from a database table. Each topping has a name and a cost, and toppings are unique. The key requirements are that no topping can be repeated in a combination, toppings must be listed in alphabetical order in the...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3198 - Find Cities in Each State

LeetCode Problem 3198 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named cities , where each row represents a relationship between a state and one of its cities. The (state, city) pair is guaranteed to be unique because it is the primary key, which means the same city will not appear twice for the same state. The task is to produce a result table...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2041 - Accepted Candidates From the Interviews

LeetCode Problem 2041 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us two database tables, Candidates and Rounds , that together describe interview performance for job candidates. The Candidates table contains one row per candidate. Each row includes the candidate's unique ID, name, years of experience, and the interview ID associated with that candidate. The Rounds table contains the scores for individual interview rounds. Each interview can...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3338 - Second Highest Salary II

LeetCode Problem 3338 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to analyze employee salary data within departments and extract all employees earning the second-highest salary in each department. The input is a table employees with three columns: emp_id , salary , and dept . Each emp_id is unique, but multiple employees may share the same salary in the same department. The output should list all...

Practice › LeetCode › LeetCode 24xx ›

LeetCode 2494 - Merge Overlapping Events in the Same Hall

LeetCode Problem 2494 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem requires us to merge overlapping events in the same hall. Each row of the HallEvents table represents an event in a particular hall with a start_day and an end_day . Events are considered overlapping if they share at least one day in common. The goal is to return a table of merged events such that no two...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3214 - Year on Year Growth Rate

LeetCode Problem 3214 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to compute the year-on-year, often abbreviated as YoY, growth rate of total spending for every product in the user_transactions table. Each row in the input table represents a single transaction. A transaction contains four important pieces of information: The unique transaction ID The product ID The amount spent in that transaction The transaction timestamp The...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3055 - Top Percentile Fraud

LeetCode Problem 3055 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to identify the top 5 percentile of insurance claims by fraud score for each state in a Fraud table. The table has three columns: policy_id , state , and fraud_score . Each policy_id is unique, and each claim has a numeric fraud_score between 0 and 1 indicating its predicted likelihood of being fraudulent. The input...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3056 - Snaps Analysis

LeetCode Problem 3056 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem requires calculating the percentage of time each age group spends on two types of snap activities: sending and opening. We are given two tables: Activities and Age . The Activities table tracks individual user activity with the time spent per action, and the Age table maps each user to an age group bucket. The goal is to...

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2893 - Calculate Orders Within Each Interval

LeetCode Problem 2893 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to process an Orders table where each row contains a minute and the number of orders received during that specific minute. We are tasked with calculating the total number of orders in intervals of six consecutive minutes. For example, minutes 1 through 6 are interval 1, minutes 7 through 12 are interval 2, and so...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2238 - Number of Times a Driver Was a Passenger

LeetCode Problem 2238 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem provides a table Rides that records rides between drivers and passengers. Each row has a unique ride_id , a driver_id , and a passenger_id . The task is to determine, for each driver, how many times that driver has appeared as a passenger in the table. In other words, for each unique driver_id , we count the...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3140 - Consecutive Available Seats II

LeetCode Problem 3140 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to analyze a cinema seating table and identify the longest continuous block of available seats. The input table is named Cinema and contains two columns: Column Meaning seat_id Unique seat number free Whether the seat is available, 1 means free and 0 means occupied A consecutive sequence means that seat IDs increase continuously by 1...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3124 - Find Longest Calls

LeetCode Problem 3124 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to analyze phone call records stored across two database tables and return the three longest calls for each call type, incoming and outgoing. The Contacts table stores information about people. Each contact has a unique id , along with their first_name and last_name . The Calls table stores call records. Each row represents a call...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2995 - Viewers Turned Streamers

LeetCode Problem 2995 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding We are given a database table called Sessions , where each row represents one user session on a platform. Every session belongs to a specific user_id , has a start and end timestamp, a unique session_id , and a session_type that can be either "Viewer" or "Streamer" . The problem asks us to identify users whose very first session...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1875 - Group Employees of the Same Salary

LeetCode Problem 1875 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This is a SQL database problem where we need to group employees into teams based on salary. The important detail is that a team is defined entirely by salary, meaning every employee in a team must have exactly the same salary, and all employees with the same salary must belong to the same team. However, not every salary forms...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3262 - Find Overlapping Shifts

LeetCode Problem 3262 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem requires counting overlapping shifts for each employee from a database table called EmployeeShifts . Each row in this table represents a single shift worked by an employee, with a start_time and an end_time . Two shifts are considered overlapping if one shift ends after another shift starts, meaning that their time intervals intersect. The goal is to...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3322 - Premier League Table Ranking III

LeetCode Problem 3322 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem requires calculating a Premier League-style ranking for teams in each season based on their match results. The input is a table SeasonStats that contains the statistics for each team per season, including the number of matches played, wins, draws, losses, goals scored, and goals conceded. Each team is uniquely identified by a combination of season_id and team_id...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3368 - First Letter Capitalization

LeetCode Problem 3368 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem provides a database table named user_content with two columns: Column Description content_id Unique identifier for each row content_text A text string containing words and spaces The task is to produce a result table that contains: The original text A transformed version of the text where: The first letter of every word is uppercase Every other letter is...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2987 - Find Expensive Cities

LeetCode Problem 2987 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 2987 - Find Expensive Cities Problem Understanding This problem provides a database table named Listings that contains information about home listings. Each row represents a single home listing and contains three fields: listing_id , a unique identifier for the listing city , the city where the home is located price , the listed price of the home The task is...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2993 - Friday Purchases I

LeetCode Problem 2993 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to compute the total amount spent on Fridays in each week of November 2023 . We are given a database table named Purchases , where each row represents a purchase made by a user on a specific date, along with the amount spent. The key requirement is that we are only interested in Fridays ,...

Practice › LeetCode › LeetCode 21xx ›

LeetCode 2153 - The Number of Passengers in Each Bus II

LeetCode Problem 2153 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem describes a simulation of passengers arriving at a bus station and buses arriving to pick them up. Each bus has a unique ID, an arrival time, and a limited capacity. Each passenger has a unique ID and an arrival time. Passengers who have arrived at or before the arrival of a bus, and who have not already...

Practice › LeetCode › LeetCode 31xx ›

LeetCode 3118 - Friday Purchase III

LeetCode Problem 3118 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to calculate the total amount of money spent by Premium and VIP members on Fridays of each week in November 2023 . The inputs are two tables: Purchases , which records the user_id , purchase_date , and amount_spend , and Users , which records the user_id and their membership type. We need to aggregate spending...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3058 - Friends With No Mutual Friends

LeetCode Problem 3058 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The Friends table represents an undirected friendship graph. Each row (user_id1, user_id2) means the two users are directly connected as friends. The problem asks us to find every friendship pair where the two users do not share any common friend. A mutual friend is a third user who is connected to both people in the pair. For example, if...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2985 - Calculate Compressed Mean

LeetCode Problem 2985 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to compute the average number of items per order from a compressed representation of order data. Instead of storing every individual order as a separate row, the table groups together orders that contain the same number of items. For each row: item_count represents how many items are in a particular type of order. order_occurrences represents...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2783 - Flight Occupancy and Waitlist Analysis

LeetCode Problem 2783 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem models airline flight bookings with limited seating capacity. The Flights table contains one row per flight. Each flight has a unique flight_id and a capacity , which represents the maximum number of passengers that can be seated on that flight. The Passengers table contains one row per passenger booking. Each passenger is associated with exactly one flight...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2084 - Drop Type 1 Orders for Customers With Type 0 Orders

LeetCode Problem 2084 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding In this problem, we are given a database table named Orders . Each row represents a single order and contains three columns: order_id , the unique identifier for the order customer_id , the customer who placed the order order_type , which is either 0 or 1 The task is to return a filtered version of the table according to...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2988 - Manager of the Largest Department

LeetCode Problem 2988 Difficulty: 🟡 Medium Topics: Database Solution You included two different problems in one message, and the second prompt overrides the first at the end. I will answer for LeetCode 2988 - Manager of the Largest Department . Problem Understanding This problem asks us to identify the manager or managers of the department(s) with the highest employee count . We are given a single database table named Employees...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2388 - Change Null Values in a Table to the Previous Value

LeetCode Problem 2388 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to process a database table, CoffeeShop , which contains two columns: id and drink . Each row represents a drink order. Some drink values may be NULL . The task is to replace every NULL in the drink column with the most recent non- NULL value from the previous rows, preserving the order of rows...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1873 - Calculate Special Bonus

LeetCode Problem 1873 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to write an SQL query that calculates a special bonus for every employee in the Employees table. Each row in the table contains three pieces of information: Column Meaning employee_id Unique identifier for the employee name Employee name salary Employee salary The task is to compute a new column called bonus according to two conditions:...

Practice › LeetCode › LeetCode 32xx ›

LeetCode 3230 - Customer Purchasing Behavior Analysis

LeetCode Problem 3230 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to analyze customer purchasing behavior using two relational tables: Transactions and Products . The Transactions table contains every purchase made by customers, including the transaction ID, customer ID, product ID, transaction date, and amount spent. The Products table contains the product catalog with product IDs, their categories, and prices. We are tasked with producing a...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1965 - Employees With Missing Information

LeetCode Problem 1965 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides two relational tables, one named Employees and another named Salaries , both keyed by employee_id . Each employee may or may not appear in both tables. The Employees table contains the employee’s name, while the Salaries table contains the employee’s salary. The task is to identify all employee_id values for which information is incomplete. An employee...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3089 - Find Bursty Behavior

LeetCode Problem 3089 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to identify users who demonstrate "bursty behavior" in their posting patterns during February 2024. Specifically, a user exhibits bursty behavior if, within any consecutive 7-day period , the number of posts they make is at least twice their average weekly posting frequency in February 2024. The input is a Posts table with columns post_id ,...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2372 - Calculate the Influence of Each Salesperson

LeetCode Problem 2372 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to calculate the total sales value generated by the customers assigned to each salesperson. We are given three database tables: The Salesperson table contains the list of salespeople. Each salesperson has a unique salesperson_id and a name . The Customer table maps customers to salespeople. Every customer belongs to exactly one salesperson through the salesperson_id...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2051 - The Category of Each Member in the Store

LeetCode Problem 2051 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 2051 - The Category of Each Member in the Store Problem Understanding This problem asks us to classify every store member into a category based on their shopping behavior. The classification depends on how often a member makes a purchase after visiting the store. We are given three database tables: Members contains the list of all members. Visits records every...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3059 - Find All Unique Email Domains

LeetCode Problem 3059 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to analyze email addresses stored in a database table and determine how many people belong to each unique email domain, but only for domains ending in .com . The Emails table contains two columns: Column Meaning id Unique identifier for each row email Full email address An email address has the general structure: username@domain For...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2394 - Employees With Deductions

LeetCode Problem 2394 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to identify employees whose monthly working time is less than the required number of hours . Each employee has a minimum number of hours they must work during October 2022 to avoid salary deductions. Employees can work in multiple sessions, and the total worked time is calculated by summing the duration of all sessions. The...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 613 - Shortest Distance in a Line

LeetCode Problem 613 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 613, Shortest Distance in a Line Problem Understanding This problem gives us a database table named Point that contains integer coordinates on the X-axis. Each row represents one point, and the column x is unique because it is the primary key. The task is to compute the smallest absolute distance between any two points in the table. Mathematically, for every...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 615 - Average Salary: Departments VS Company

LeetCode Problem 615 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to compare the average salary of each department against the company's overall average salary for each month. We are given two tables: Salary and Employee . The Salary table records the monthly salary of each employee along with a date, while the Employee table maps employees to their department. The goal is to produce a...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1715 - Count Apples and Oranges

LeetCode Problem 1715 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to compute the total number of apples and oranges across all boxes, taking into account that some boxes may contain a chest. The Boxes table gives us the count of apples and oranges in each box, and optionally the chest_id if a chest is present in that box. The Chests table gives the count of...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1527 - Patients With a Condition

LeetCode Problem 1527 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to query a database table Patients and return the records of patients who have Type I Diabetes. Each patient record includes a patient_id , patient_name , and a conditions column. The conditions column may contain zero or more condition codes separated by spaces. A patient has Type I Diabetes if any of their condition codes...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1635 - Hopper Company Queries I

LeetCode Problem 1635 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to generate monthly statistics for the year 2020 using information from three database tables: Drivers , Rides , and AcceptedRides . The first required statistic is active_drivers . For each month of 2020, we must count how many drivers had already joined the company by the end of that month. A driver is considered active...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1699 - Number of Calls Between Two Persons

LeetCode Problem 1699 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem provides a database table named Calls , where each row represents a phone call between two people. The table contains three columns: Column Meaning from_id The caller to_id The receiver duration Duration of the call The important detail is that calls are directional in the raw data, but the final result should treat calls between two people...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1831 - Maximum Transaction Each Day

LeetCode Problem 1831 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us a table named Transactions where each row represents a financial transaction. Every transaction has a unique transaction_id , a timestamp stored in the day column, and an integer amount . The goal is to find the transaction IDs whose amount is the highest for their respective calendar day. The important detail is that the day...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1549 - The Most Recent Orders for Each Product

LeetCode Problem 1549 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to find the most recent order for every product that has been ordered at least once. We are given three database tables: The Customers table contains customer information. The Orders table stores every order placed by customers. The Products table stores product information. The important table for this problem is Orders , because it contains:...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1142 - User Activity for the Past 30 Days II

LeetCode Problem 1142 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to compute the average number of sessions per user over a specific 30-day period ending on 2019-07-27 . Each row in the Activity table represents an activity a user performed in a session on a particular date. A single session can have multiple activities, and the table may contain duplicate rows. A session counts for...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1364 - Number of Trusted Contacts of a Customer

LeetCode Problem 1364 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to analyze relationships between customers, their contacts, and invoices. We are given three tables: Customers , Contacts , and Invoices . The Customers table identifies each customer by customer_id along with their name and email. The Contacts table contains a list of contacts for each customer, with user_id referring to the customer and each contact...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1709 - Biggest Window Between Visits

LeetCode Problem 1709 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The UserVisits table stores records of when users visited a retailer. Each row contains a user_id and a visit_date . A user may appear multiple times because they can visit on many different days. The goal is to compute, for every user, the largest number of days between consecutive visits. For the final visit of a user, the comparison...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2026 - Low-Quality Problems

LeetCode Problem 2026 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Problems . Each row represents a LeetCode problem and contains three columns: Column Meaning problem_id Unique identifier for the problem likes Number of users who liked the problem dislikes Number of users who disliked the problem We must identify all problems whose like percentage is strictly less than 60% . The...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 571 - Find Median Given Frequency of Numbers

LeetCode Problem 571 Difficulty: 🔴 Hard Topics: Database Solution LeetCode 571 - Find Median Given Frequency of Numbers Problem Understanding This problem provides a compressed representation of a dataset instead of listing every number individually. The table Numbers contains two columns: num , the actual number frequency , how many times that number appears If we expanded the table into a full sorted array, each num would appear exactly frequency...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1126 - Active Businesses

LeetCode Problem 1126 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 1126 - Active Businesses Problem Understanding The problem gives us a database table named Events . Each row represents how many times a certain type of event occurred for a particular business. The table contains three columns: Column Meaning business_id The identifier of the business event_type The category of event occurrences Number of times that event occurred The pair (business_id,...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1757 - Recyclable and Low Fat Products

LeetCode Problem 1757 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem gives us a database table named Products . Each row represents a product and contains three columns: Column Meaning product_id Unique identifier for the product low_fats 'Y' if the product is low fat, otherwise 'N' recyclable 'Y' if the product is recyclable, otherwise 'N' The task is to return the IDs of products that satisfy both conditions...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 577 - Employee Bonus

LeetCode Problem 577 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding In this problem, we are given two database tables, Employee and Bonus , and we need to produce a result table containing employees who meet one of two conditions: Their bonus is less than 1000 . They do not have a bonus record at all. The output should include only two columns: the employee's name and their bonus ....

Practice › LeetCode › LeetCode 06xx ›

LeetCode 619 - Biggest Single Number

LeetCode Problem 619 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named MyNumbers that contains a single column, num . The table may contain duplicate values because there is no primary key restriction. Our task is to find the largest number that appears exactly once in the table. A number is considered a "single number" if its frequency in the table is exactly...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1141 - User Activity for the Past 30 Days I

LeetCode Problem 1141 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 1141 - User Activity for the Past 30 Days I Problem Understanding This problem asks us to compute the number of distinct active users for each day within a fixed 30 day window. The window ends on 2019-07-27 , inclusive, which means we only consider activity dates from 2019-06-28 through 2019-07-27 . The Activity table records user interactions on a...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 614 - Second Degree Follower

LeetCode Problem 614 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to identify second-degree followers from a social network represented by a single table Follow . The table contains two columns: followee and follower . Each row indicates that a user ( follower ) follows another user ( followee ). Importantly, each user cannot follow themselves, and the combination of followee and follower is unique. A...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1633 - Percentage of Users Attended a Contest

LeetCode Problem 1633 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to calculate the percentage of users who attended each contest . We are given two tables: Users and Register . The Users table contains all users, each with a unique user_id . The Register table contains records of which user registered for which contest, using contest_id and user_id . The goal is to compute the...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1045 - Customers Who Bought All Products

LeetCode Problem 1045 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to identify all customers who have purchased every product listed in the Product table. In other words, a customer is eligible for the output if, for each product_key in the Product table, there exists a corresponding row in the Customer table where that customer bought that product. The input consists of two relational tables. The...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 177 - Nth Highest Salary

LeetCode Problem 177 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to write a SQL function that returns the nth highest distinct salary from the Employee table. The table contains two columns: Column Meaning id Unique employee identifier salary Employee salary The key detail is that the salary must be distinct . Multiple employees may share the same salary, but duplicate salary values should only be...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1285 - Find the Start and End Number of Continuous Ranges

LeetCode Problem 1285 Difficulty: 🟡 Medium Topics: Database Solution Here’s a full technical solution guide for LeetCode 1285 following your requested structure and formatting: Problem Understanding The problem asks us to find contiguous ranges of integers in a database table called Logs . Each row in the table contains a unique integer log_id . A contiguous range is a sequence of consecutive integers without gaps. For example, if the table...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1270 - All People Report to the Given Manager

LeetCode Problem 1270 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to identify all employees in a company who directly or indirectly report to the head of the company, whose employee_id is 1. The input is a table Employees containing three columns: employee_id , employee_name , and manager_id . Each row defines an employee and the manager they report to. The expected output is a table...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 180 - Consecutive Numbers

LeetCode Problem 180 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to find numbers in a table that appear at least three times consecutively in order of their id . The table Logs consists of two columns: id and num , where id is an auto-incrementing primary key and num is a string representing a number. The consecutive property is determined by the order of id...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 511 - Game Play Analysis I

LeetCode Problem 511 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to determine the first day each player logged into a game based on a table called Activity . Each row of this table contains a player_id , the device_id used, the event_date on which the player logged in, and the number of games_played during that session. The player_id and event_date combination is unique, so no...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1355 - Activity Participants

LeetCode Problem 1355 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to analyze participation counts for different activities and return only the activities whose participant counts are neither the highest nor the lowest among all activities. We are given two database tables: The Friends table records which friend participates in which activity. Each row represents one friend and exactly one activity. The Activities table contains the...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1741 - Find Total Time Spent by Each Employee

LeetCode Problem 1741 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to calculate the total time each employee spends in the office per day based on a table of their in and out times. Each row in the Employees table represents a single period that an employee was in the office, with columns for emp_id , event_day , in_time , and out_time . The in_time and...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 178 - Rank Scores

LeetCode Problem 178 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us a database table named Scores that contains two columns: id and score . Each row represents the score achieved in a game. The id column is unique for every row, while the score column may contain duplicate values because multiple players or games can have the same score. The goal is to assign a rank...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1158 - Market Analysis I

LeetCode Problem 1158 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to analyze purchasing activity on an online shopping platform. We are given three database tables: Users , Orders , and Items . Our task is to produce a result that contains every user, their join date, and the number of orders they placed as a buyer during the year 2019. The key detail is that...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 620 - Not Boring Movies

LeetCode Problem 620 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to query a database table called Cinema and return a filtered set of movies based on two conditions: the movie ID must be odd, and its description must not be "boring" . The result must then be sorted in descending order by the movie's rating . In other words, for every row in the...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1193 - Monthly Transactions I

LeetCode Problem 1193 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem is asking us to produce aggregated statistics on transactions, grouped by month and country, from the Transactions table. Each row in the table represents a transaction and contains the following columns: id (primary key), country (string), state (enum of approved or declined ), amount (integer), and trans_date (date). For each combination of month and country, we are...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1811 - Find Interview Candidates

LeetCode Problem 1811 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem is asking us to identify users who qualify as interview candidates based on their performance in LeetCode contests. We are provided two tables: Contests and Users . The Contests table lists contest IDs along with the user IDs of the gold, silver, and bronze medalists for each contest. The Users table contains the user information including user_id...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 603 - Consecutive Available Seats

LeetCode Problem 603 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Cinema with two columns: Column Meaning seat_id Unique identifier for a seat free Whether the seat is available, where 1 means free and 0 means occupied We need to find all seats that are part of at least one consecutive sequence of free seats. Two seats are consecutive if their seat_id...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 610 - Triangle Judgement

LeetCode Problem 610 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to determine, for each row in a table called Triangle , whether the three given line segments can form a valid triangle. Each row contains three integers x , y , and z representing the lengths of the segments. The expected output is a new table that includes all original columns plus a triangle...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1581 - Customer Who Visited but Did Not Make Any Transactions

LeetCode Problem 1581 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us two database tables, Visits and Transactions . The Visits table records every time a customer visited the mall. Each row contains a unique visit_id and the customer_id associated with that visit. The Transactions table records purchases made during a visit. Each transaction references a visit_id , meaning that a single visit can have zero, one,...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1076 - Project Employees II

LeetCode Problem 1076 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify the project or projects that have the largest number of employees assigned to them. We are given two database tables. The Project table stores relationships between projects and employees. Each row means that a particular employee is working on a particular project. The pair (project_id, employee_id) is unique, which guarantees that the same...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 626 - Exchange Seats

LeetCode Problem 626 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to swap the seat IDs of every two consecutive students in a classroom. The input is a table called Seat with two columns: id , which is a unique integer representing the seat number, and student , which is a string representing the student's name. The IDs are consecutive integers starting from 1, which guarantees...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3053 - Classifying Triangles by Lengths

LeetCode Problem 3053 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem requires classifying triangles based on the lengths of their three sides, represented by the columns A , B , and C in the Triangles table. Each row in the table represents a potential triangle. The output should identify each triangle as one of four types: Equilateral , Isosceles , Scalene , or Not A Triangle . A...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 597 - Friend Requests I: Overall Acceptance Rate

LeetCode Problem 597 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to compute the overall acceptance rate of friend requests in a social network system. Two database tables are provided. The first table, FriendRequest , stores all friend requests that users sent to each other. The second table, RequestAccepted , stores requests that were accepted. The acceptance rate is defined as: $\text{Acceptance Rate} = \frac{\text{Number of...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 182 - Duplicate Emails

LeetCode Problem 182 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Person with two columns: Column Description id A unique integer identifier for each row email The email address associated with that row The goal is to find all email addresses that appear more than once in the table. In other words, we need to identify duplicate email values. The output should...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1164 - Product Price at a Given Date

LeetCode Problem 1164 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem provides a database table named Products , where each row represents a price update for a product on a specific date. The columns are: Column Meaning product_id The identifier of the product new_price The new price assigned to the product change_date The date when the new price became effective The pair (product_id, change_date) is guaranteed to be...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1613 - Find the Missing IDs

LeetCode Problem 1613 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us a database table named Customers , where each row contains a unique customer_id and a corresponding customer_name . Our task is to identify all missing customer IDs between 1 and the maximum customer_id currently present in the table. In other words, suppose the largest customer ID in the table is max_id . We must examine...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 176 - Second Highest Salary

LeetCode Problem 176 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to retrieve the second highest distinct salary from the Employee table. The key word here is distinct . We are not looking for the second row after sorting salaries, we are looking for the second unique salary value. This distinction matters because duplicate salaries should only count once. For example, if the salaries are: [100,...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1789 - Primary Department for Each Employee

LeetCode Problem 1789 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Employee that stores information about which departments employees belong to. Each row contains three values: Column Meaning employee_id The employee identifier department_id A department the employee belongs to primary_flag Whether this department is the employee's primary department The combination (employee_id, department_id) is unique, meaning the same employee cannot appear twice for the...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1398 - Customers Who Bought Products A and B but Not C

LeetCode Problem 1398 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to identify customers who meet a very specific purchasing pattern. We are given two tables: Customers and Orders . The Customers table contains the unique customer_id and the corresponding customer_name . The Orders table records purchases with order_id , customer_id , and product_name . Our task is to find customers who bought both product "A"...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 262 - Trips and Users

LeetCode Problem 262 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to compute the daily cancellation rate for taxi trips over a fixed date range, specifically from "2013-10-01" to "2013-10-03" . We are given two database tables: Trips , which stores information about every taxi trip request Users , which stores user metadata such as whether a user is banned Each trip contains a client, a...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1322 - Ads Performance

LeetCode Problem 1322 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to calculate the Click-Through Rate, abbreviated as CTR, for every advertisement stored in the Ads table. The table contains three columns: Column Meaning ad_id Identifier of the advertisement user_id Identifier of the user interacting with the ad action The interaction type, either Clicked , Viewed , or Ignored The CTR formula is: $$CTR = \frac{\text{number...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1174 - Immediate Food Delivery II

LeetCode Problem 1174 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem provides a Delivery table that records food delivery orders. Each row represents a single order placed by a customer. Along with the order date, each customer also specifies a preferred delivery date. If the preferred delivery date is exactly the same as the order date, the order is considered an immediate order. Otherwise, it is considered a...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 585 - Investments in 2016

LeetCode Problem 585 Difficulty: 🟡 Medium Topics: Database Solution Here’s a full, detailed technical solution guide for LeetCode 585 following your exact formatting rules: Problem Understanding The problem presents an Insurance table containing policyholder information, including a unique policy ID ( pid ), investment values for 2015 ( tiv_2015 ) and 2016 ( tiv_2016 ), and location coordinates ( lat and lon ). The task is to calculate the sum...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 596 - Classes With at Least 5 Students

LeetCode Problem 596 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem is asking us to find classes in a school database that have at least five students enrolled. The input is a table named Courses with two columns: student and class . Each row represents one student being enrolled in one class. The primary key of this table is the combination of (student, class) , so there are...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 618 - Students Report By Geography

LeetCode Problem 618 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to transform a table of student names and their continents into a pivoted report, where each continent becomes a column and the student names appear alphabetically under their respective continents. The input is a Student table containing two columns: name and continent . This table may include duplicate entries, which should not affect the pivot...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2010 - The Number of Seniors and Juniors to Join the Company II

LeetCode Problem 2010 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to simulate a hiring process with a fixed salary budget of $70,000, where candidates are classified as either "Senior" or "Junior" and each has a unique salary. The hiring rules are strict: we must first attempt to hire as many seniors as possible, always picking the one with the smallest salary first, until we can...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1677 - Product's Worth Over Invoices

LeetCode Problem 1677 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to calculate aggregate monetary information for each product based on invoices. We have two tables: Product and Invoice . The Product table contains a unique product_id and the name of the product. The Invoice table contains individual invoices for products, including amounts for rest (amount left to pay), paid , canceled , and refunded ....

Practice › LeetCode › LeetCode 05xx ›

LeetCode 512 - Game Play Analysis II

LeetCode Problem 512 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Activity . Each row represents one login session for a player on a specific date. The table contains four columns: Column Meaning player_id The unique identifier for a player device_id The device used during that login session event_date The date of the login games_played Number of games played during that session The...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1070 - Product Sales Analysis III

LeetCode Problem 1070 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to analyze sales data stored in a Sales table and extract the records corresponding to the first year each product was sold . Specifically, for each product_id , we need to determine the earliest year in which it appears in the table and return all sales records for that product in that year. The input...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 184 - Department Highest Salary

LeetCode Problem 184 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to find employees with the highest salary in each department from a company database. The input consists of two relational tables: Employee and Department . The Employee table contains employee details, including id , name , salary , and departmentId . The departmentId is a foreign key linking the employee to the Department table. The...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1661 - Average Time of Process per Machine

LeetCode Problem 1661 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Activity , which stores information about processes executed on different machines. Each process has exactly two records: A "start" record, indicating when the process began An "end" record, indicating when the process finished Each row contains four columns: Column Meaning machine_id The machine executing the process process_id The specific process running on...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1484 - Group Sold Products By The Date

LeetCode Problem 1484 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Activities with two columns: Column Meaning sell_date The date a product was sold product The name of the product The table does not contain a primary key, which means duplicate rows may exist. For example, the same product could appear multiple times on the same date. We need to generate a...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 569 - Median Employee Salary

LeetCode Problem 569 Difficulty: 🔴 Hard Topics: Database Solution LeetCode 569, Median Employee Salary Problem Understanding The problem gives us an Employee table containing three columns: Column Meaning id Unique employee identifier company Company name salary Employee salary We need to return the row or rows that correspond to the median salary for each company. The important detail is that salaries must first be sorted in ascending order. If two...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1511 - Customer Order Frequency

LeetCode Problem 1511 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify customers who consistently spend at least $100 in each of two consecutive months, June and July of 2020. We have three tables: Customers , which lists customer details; Product , which lists products and their prices; and Orders , which logs all purchases by customers with the quantity and date. The input represents...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1336 - Number of Transactions per Visit

LeetCode Problem 1336 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to analyze two database tables, Visits and Transactions , and compute how many visitors performed a given number of transactions per visit. Each row in the Visits table represents a unique visit by a user on a specific date. The Transactions table may contain multiple rows per user per date, indicating multiple transactions on the...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 578 - Get Highest Answer Rate Question

LeetCode Problem 578 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to analyze user interaction data stored in the SurveyLog table and determine which question has the highest answer rate. The table records actions performed by users during survey sessions. Every row represents a single interaction with a question. The important columns for this problem are: Column Meaning question_id The question being interacted with action The...

Practice › LeetCode › LeetCode 19xx ›

LeetCode 1949 - Strong Friendship

LeetCode Problem 1949 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us a table named Friendship , where every row represents a friendship relationship between two users. Each friendship is stored only once because the problem guarantees that user1_id < user2_id . We are asked to identify all pairs of users whose friendship is considered "strong". A friendship between users x and y is strong if they...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1777 - Product's Price for Each Store

LeetCode Problem 1777 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a table named Products , where each row represents the price of a specific product in a specific store. Every row contains three values: product_id , identifying the product store , identifying which store sells the product price , representing the price of that product in that store The (product_id, store) pair is guaranteed to be...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1294 - Weather Type in Each Country

LeetCode Problem 1294 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to determine the weather type for each country during November 2019 , based on the average weather_state recorded in that month. We are given two database tables: The Countries table stores information about countries. Each row contains a unique country_id and its corresponding country_name . The Weather table stores daily weather information for countries. Each...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1225 - Report Contiguous Dates

LeetCode Problem 1225 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to analyze a system that runs one task per day over a fixed period, from 2019-01-01 to 2019-12-31 . Each day, the task either succeeds or fails. We are given two tables: Failed and Succeeded , each containing dates when the tasks failed or succeeded, respectively. The dates are unique within each table. The goal...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1211 - Queries Quality and Percentage

LeetCode Problem 1211 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Queries . Each row represents the outcome of running a particular query against a database. The columns are: Column Meaning query_name The name of the query group result The returned result string position The rank or position of the result rating A score from 1 to 5 evaluating the result quality...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1384 - Total Sales Amount by Year

LeetCode Problem 1384 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This is a SQL database problem where we need to calculate the total sales amount per product for each year , even when a sales period spans across multiple calendar years. We are given two tables: The Product table contains metadata about products. Each row represents a unique product with its product_id and product_name . The Sales table contains...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1693 - Daily Leads and Partners

LeetCode Problem 1693 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named DailySales , where each row represents a sale event involving a product manufacturer ( make_name ), a lead ( lead_id ), and a partner ( partner_id ) on a specific date ( date_id ). The goal is to compute, for every unique combination of date_id and make_name , two values: The number...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1495 - Friendly Movies Streamed Last Month

LeetCode Problem 1495 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to find the titles of movies that satisfy three separate conditions at the same time. First, the content must be marked as kid-friendly. In the Content table, this is represented by the column Kids_content = 'Y' . Second, the content must actually be a movie. The content_type column tells us whether a piece of content...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1407 - Top Travellers

LeetCode Problem 1407 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 1407 - Top Travellers Problem Understanding This problem gives us two database tables, Users and Rides . The Users table contains information about each user. Every user has a unique id and a corresponding name . The Rides table contains ride records. Each ride has its own unique id , a user_id indicating which user took the ride, and a...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1241 - Number of Comments per Post

LeetCode Problem 1241 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to analyze a database table named Submissions and determine how many unique comments belong to each post. The table contains two columns: Column Meaning sub_id The ID of the current submission parent_id The parent submission ID A row represents either a post or a comment: If parent_id is NULL , the row is a post....

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1479 - Sales by Day of the Week

LeetCode Problem 1479 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to generate a sales report that summarizes the total quantity of items sold for each category on each day of the week. The data is provided in two tables: Orders and Items . The Orders table contains transactional information, including which customer bought which item, in what quantity, and on what date. The Items table...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1280 - Students and Examinations

LeetCode Problem 1280 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to generate a complete report showing how many times every student attended every subject examination. We are given three database tables: Students , which stores each student's ID and name. Subjects , which stores every subject offered in the school. Examinations , which records every exam attendance entry. The important detail is that the Examinations...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2308 - Arrange Table by Gender

LeetCode Problem 2308 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to rearrange the rows of a Genders table in a specific repeating order while maintaining internal sorting. The table has two columns: user_id and gender . The user_id is unique for each row, and the gender column can take one of three values: 'female' , 'male' , or 'other' . The table guarantees that there...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1445 - Apples & Oranges

LeetCode Problem 1445 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem provides a database table named Sales that stores the number of fruits sold on each day. Each row represents a single fruit sale summary for a specific date. The table has three columns: Column Meaning sale_date The date of the sales fruit Either "apples" or "oranges" sold_num Number of units sold The primary key is (sale_date, fruit)...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 584 - Find Customer Referee

LeetCode Problem 584 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a Customer table with three columns: id , name , and referee_id . Each row represents a customer, their unique identifier ( id ), their name, and optionally the id of the customer who referred them. A null value in referee_id indicates that the customer was not referred by anyone. The task is to identify all...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1082 - Sales Analysis I

LeetCode Problem 1082 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify the seller or sellers who generated the highest total sales revenue. We are given two database tables: Product and Sales . The Product table contains information about products, including their IDs, names, and unit prices. The Sales table records transactions, where each row represents a sale and includes details such as the seller...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1132 - Reported Posts II

LeetCode Problem 1132 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to calculate the average daily percentage of posts that were removed after being reported as spam. We are given two tables: Actions and Removals . The Actions table records user interactions with posts, including views, likes, shares, reports, and other reactions. The extra column contains optional information about the action, such as the reason for...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 580 - Count Student Number in Departments

LeetCode Problem 580 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to determine how many students are enrolled in each department, including departments that currently have no students. We are given two tables: Student and Department . The Student table contains details about students such as their student_id , student_name , gender , and dept_id . The dept_id references the Department table, which contains dept_id and...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1050 - Actors and Directors Who Cooperated At Least Three Times

LeetCode Problem 1050 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify every (actor_id, director_id) pair where an actor and a director have collaborated at least three times. The input is a database table named ActorDirector . Each row represents one collaboration event between an actor and a director. The table contains three columns: actor_id , which uniquely identifies an actor director_id , which uniquely...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 570 - Managers with at Least 5 Direct Reports

LeetCode Problem 570 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The Employee table represents a company hierarchy. Every row corresponds to one employee and contains four pieces of information: Column Meaning id Unique employee identifier name Employee name department Department the employee belongs to managerId The id of this employee’s manager If managerId is NULL , the employee does not report to anyone and is therefore at the top...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1393 - Capital Gain/Loss

LeetCode Problem 1393 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The Stocks table records stock trading activity. Each row represents either a Buy or Sell operation for a specific stock on a particular day, along with the transaction price. The table contains four columns: Column Meaning stock_name The name of the stock operation Either 'Buy' or 'Sell' operation_day The day the transaction occurred price The transaction price The problem...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 607 - Sales Person

LeetCode Problem 607 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to find the names of all salespeople who have never handled an order for the company named "RED" . We are given three database tables: SalesPerson contains information about each salesperson, including their unique sales_id and name . Company contains company information, including com_id and company name . Orders records every order, linking a salesperson...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1113 - Reported Posts

LeetCode Problem 1113 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to determine the number of posts that were reported yesterday grouped by the reason for the report. We are given an Actions table where each row represents a user performing an action on a post, with the action type recorded in the action column and optional extra information in the extra column. In this...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 175 - Combine Two Tables

LeetCode Problem 175 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to combine two relational database tables, Person and Address , in such a way that we report each person's first name, last name, city, and state. The Person table contains identifiers and names of people, while the Address table contains identifiers, the corresponding personId , and the city and state of that person. Importantly,...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1205 - Monthly Transactions II

LeetCode Problem 1205 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 1205 - Monthly Transactions II Problem Understanding This problem asks us to generate a monthly financial summary for each country using information from two database tables: Transactions and Chargebacks . The Transactions table stores incoming transactions. Each transaction has a unique ID, a country, a state ( approved or declined ), an amount, and the transaction date. The Chargebacks table...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1459 - Rectangles Area

LeetCode Problem 1459 Difficulty: 🟡 Medium Topics: Database Solution You included two different problems in one message, and the second prompt supersedes the first. I will provide the detailed technical solution guide for LeetCode 1459 - Rectangles Area following your exact formatting requirements. Problem Understanding This problem asks us to identify all possible axis-aligned rectangles that can be formed using pairs of points from a database table. Each point in...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1084 - Sales Analysis III

LeetCode Problem 1084 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to identify products that were sold only during the first quarter of 2019, meaning between 2019-01-01 and 2019-03-31 , inclusive. We are provided with two tables: Product and Sales . The Product table lists all products along with their IDs and unit prices, while the Sales table lists individual sales transactions with the product_id ,...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1303 - Find the Team Size

LeetCode Problem 1303 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named Employee , where every row represents a single employee and the team they belong to. The table contains two columns: Column Meaning employee_id Unique identifier for an employee team_id Identifier of the team the employee belongs to The task is to compute the size of each employee's team. In other words, for...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1069 - Product Sales Analysis II

LeetCode Problem 1069 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to calculate the total quantity sold for each product based on records in the Sales table. The Sales table contains transaction level information. Each row represents a sale of a specific product in a given year, along with the quantity sold and the unit price. Since a product can appear in multiple rows, potentially across...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 183 - Customers Who Never Order

LeetCode Problem 183 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem is asking us to identify all customers from a Customers table who have never placed an order according to the Orders table. In other words, we are looking for entries in Customers that do not have a corresponding customerId in the Orders table. The input consists of two tables: Customers and Orders . Customers has an id...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1369 - Get the Second Most Recent Activity

LeetCode Problem 1369 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem gives us a database table named UserActivity that stores activity periods for different users. Each row contains four fields: Column Meaning username The user who performed the activity activity The name of the activity startDate When the activity started endDate When the activity ended A single user may have multiple activity records, and the records are ordered...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1251 - Average Selling Price

LeetCode Problem 1251 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to compute the average selling price for every product based on two tables: Prices and UnitsSold . The Prices table tells us how much a product costs during a specific date range. Each row contains a product_id , a start_date , an end_date , and the price for that period. A product may have multiple...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1454 - Active Users

LeetCode Problem 1454 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to identify active users from a database containing two tables: Accounts and Logins . The Accounts table lists all users with their id and name , and the Logins table records all login events, including duplicates and multiple logins per day for the same user. A user is defined as active if they have logged...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3054 - Binary Tree Nodes

LeetCode Problem 3054 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to classify nodes in a binary tree based on their role in the tree structure. The input is represented as a table Tree with two columns: N representing the node value, and P representing the parent node value. A null parent indicates that the node is the root. Each node is guaranteed to have a...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 579 - Find Cumulative Salary of an Employee

LeetCode Problem 579 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to compute a cumulative salary summary for each employee based on their monthly salaries over the year 2020. The input is a table Employee where each row contains an employee id , the month (1 through 12), and the salary for that month. Each (id, month) combination is unique. The cumulative salary summary is calculated...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1795 - Rearrange Products Table

LeetCode Problem 1795 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The Products table stores product prices across three different stores. Each row represents one product, identified by product_id , and each store column contains the product's price in that specific store. The table has this structure: Column Meaning product_id Unique identifier for the product store1 Price of the product in store1 store2 Price of the product in store2 store3...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1651 - Hopper Company Queries III

LeetCode Problem 1651 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem requires computing a rolling 3-month average of ride distance and ride duration from ride data in a ride-hailing company database. We are given three tables: Drivers , Rides , and AcceptedRides . Drivers provides driver information and join dates, Rides contains requested rides with dates, and AcceptedRides contains rides that were actually accepted by drivers, along with...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 534 - Game Play Analysis III

LeetCode Problem 534 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem is asking us to track cumulative game activity for each player. Specifically, we are given an Activity table where each row represents a single login session for a player on a specific device and date, along with the number of games played during that session. The goal is to produce a report that shows, for each player...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1173 - Immediate Food Delivery I

LeetCode Problem 1173 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking to calculate the percentage of immediate food deliveries from a delivery table. An immediate delivery is defined as one where the customer_pref_delivery_date matches the order_date . The input is a table named Delivery with columns delivery_id , customer_id , order_date , and customer_pref_delivery_date . Each row represents a single delivery order with its preferred delivery...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2020 - Number of Accounts That Did Not Stream

LeetCode Problem 2020 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to analyze two database tables, Subscriptions and Streams , and determine how many accounts purchased a subscription during the year 2021 but never streamed any content during 2021. The Subscriptions table stores subscription intervals for each account. Each row contains: account_id , the unique identifier for the account start_date , the beginning of the subscription...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1127 - User Purchase Platform

LeetCode Problem 1127 Difficulty: 🔴 Hard Topics: Database Solution LeetCode 1127, User Purchase Platform Problem Understanding The Spending table records purchases made by users on an e-commerce platform. Every row represents one user's spending on a specific date using either the mobile platform or the desktop platform. The table has four columns: Column Meaning user_id The user making the purchase spend_date The date of the purchase platform Either mobile or...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1098 - Unpopular Books

LeetCode Problem 1098 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to identify books from a Books table that are considered unpopular based on their sales in the last year, relative to a fixed "today" date of 2019-06-23 . Specifically, a book is unpopular if it sold less than 10 copies in the period from 2018-06-23 to 2019-06-23 . Additionally, we must exclude books that have...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1327 - List the Products Ordered in a Period

LeetCode Problem 1327 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to list all products that have been ordered in February 2020 with a total quantity of at least 100 units. We are given two tables: Products and Orders . The Products table contains metadata about each product including its unique product_id and product_name . The Orders table records every order of products with the product_id...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1075 - Project Employees I

LeetCode Problem 1075 Difficulty: 🟢 Easy Topics: Database Solution LeetCode 1075, Project Employees I Problem Understanding This problem provides two database tables, Project and Employee . The Project table represents which employees are assigned to which projects. Each row contains a project_id and an employee_id . Since the pair (project_id, employee_id) is the primary key, the same employee cannot appear more than once for the same project. The Employee table...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1440 - Evaluate Boolean Expression

LeetCode Problem 1440 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to evaluate boolean expressions stored in a database table. We are given two tables: Variables , which stores variable names and their corresponding integer values, and Expressions , which stores boolean expressions made up of two operands and a comparison operator. Each row in Expressions represents a condition of the form: left_operand operator right_operand For...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1517 - Find Users With Valid E-Mails

LeetCode Problem 1517 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to query a database table named Users and return only the rows corresponding to users whose e-mail addresses are considered valid according to a very specific format. Each row in the Users table contains three columns: user_id , a unique integer identifier for each user name , the user's name mail , the user's e-mail...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1112 - Highest Grade For Each Student

LeetCode Problem 1112 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 1112 - Highest Grade For Each Student Problem Understanding The problem gives us a database table named Enrollments . Each row represents a student taking a course and receiving a grade for that course. The table has three columns: Column Meaning student_id The unique identifier of a student course_id The unique identifier of a course grade The student's grade in...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1194 - Tournament Winners

LeetCode Problem 1194 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to determine the winner in each group of players based on their accumulated points across multiple matches. We are given two tables: Players and Matches . The Players table maps each player to a group, while the Matches table records each match's score between two players, where all matches occur within the same group. The...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1212 - Team Scores in Football Tournament

LeetCode Problem 1212 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to compute the total points for each football team after a series of matches in a tournament. The scoring rules are standard: a win gives 3 points, a draw gives 1 point, and a loss gives 0 points. The input consists of two tables: Teams and Matches . The Teams table contains the unique identifiers...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1149 - Article Views II

LeetCode Problem 1149 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us a database table named Views . Each row represents a single viewing event where a user viewed an article on a specific date. The columns are: Column Meaning article_id The article being viewed author_id The author who wrote the article viewer_id The user who viewed the article view_date The date of the view The task...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1683 - Invalid Tweets

LeetCode Problem 1683 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem gives us a database table named Tweets with two columns: Column Description tweet_id Unique identifier for each tweet content The text content of the tweet The task is to return the IDs of all invalid tweets. A tweet is considered invalid if the number of characters in its content is strictly greater than 15 . In other...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 612 - Shortest Distance in a Plane

LeetCode Problem 612 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem gives us a database table named Point2D , where every row represents a unique point on a 2D Cartesian plane. Each point contains two integer coordinates, x and y . The pair (x, y) is guaranteed to be unique because it is the primary key. We are asked to compute the shortest Euclidean distance between any two...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3052 - Maximize Items

LeetCode Problem 3052 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem requires determining how many items can be stored in a warehouse with a limited square footage of 500,000 . The items are categorized as either prime_eligible or not_prime . The goal is to first maximize the number of prime_eligible items stored, then use any remaining space to store as many not_prime items as possible. Each item has...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1565 - Unique Orders and Customers Per Month

LeetCode Problem 1565 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem requires analyzing a table of orders to calculate monthly statistics. Specifically, for each unique month present in the Orders table, we need to determine two metrics: the number of unique orders and the number of unique customers whose orders have an invoice greater than 20. The input consists of a table with four columns: order_id (unique identifier),...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1747 - Leetflex Banned Accounts

LeetCode Problem 1747 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to identify suspicious accounts in the LogInfo table. Each row represents a login session for a user account, including the account ID, the IP address used during the session, and the login and logout timestamps. An account should be banned if there exists at least one moment in time where the same account is simultaneously...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1097 - Game Play Analysis V

LeetCode Problem 1097 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem requires calculating the day one retention metric for a game based on user activity data. The input is an Activity table, where each row represents a login session of a player on a particular day, including the device used and the number of games played. The install date for a player is defined as the date of...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 185 - Department Top Three Salaries

LeetCode Problem 185 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This is a SQL database problem where we need to identify the employees who belong to the top three unique salaries within each department . The input consists of two tables: The Employee table stores information about each employee, including: id , a unique identifier for the employee name , the employee's name salary , the employee's salary departmentId...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1841 - League Statistics

LeetCode Problem 1841 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to compute a complete league table from two database tables, Teams and Matches . The Teams table contains the identity of each team in the league. Each row represents one team and includes a unique team_id and the corresponding team_name . The Matches table contains the results of games played between teams. Every row describes...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1341 - Movie Rating

LeetCode Problem 1341 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 1341 - Movie Rating Problem Understanding This problem works with three relational database tables: Movies , Users , and MovieRating . The goal is to produce a result containing exactly two rows. The first row should contain the name of the user who rated the greatest number of movies. If multiple users rated the same maximum number of movies, we...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1571 - Warehouse Manager

LeetCode Problem 1571 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to calculate the total storage volume occupied by products inside each warehouse. We are given two database tables: The Warehouse table tells us which products are stored in each warehouse and how many units of each product exist there. Warehouse(name, product_id, units) The Products table stores the physical dimensions of every product. Products(product_id, product_name, Width,...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1083 - Sales Analysis II

LeetCode Problem 1083 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify all buyers who purchased the product named S8 but never purchased the product named iPhone . We are given two tables: The Product table stores information about products. Each row contains a unique product_id , the product name, and its unit price. The Sales table stores sales transactions. Each row represents a purchase...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1729 - Find Followers Count

LeetCode Problem 1729 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to determine, for each user in a social media application, how many followers they have. The input is a table called Followers with two columns: user_id and follower_id . Each row represents a relationship where follower_id follows user_id . The combination (user_id, follower_id) is unique, so there are no duplicate follower entries for a...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1731 - The Number of Employees Which Report to Each Employee

LeetCode Problem 1731 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The Employees table stores information about employees inside a company. Each row represents one employee and contains four columns: Column Meaning employee_id Unique identifier for the employee name Employee name reports_to The manager this employee reports to age Employee age If reports_to is NULL , that employee does not report to anyone. The problem defines a manager as any...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1159 - Market Analysis II

LeetCode Problem 1159 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to determine, for every user in the marketplace system, whether the brand of the second item they sold matches their favorite brand . The database contains three tables: The Users table stores user information, including their favorite_brand . The Orders table records purchases and sales. Each order includes a seller_id , item_id , and order_date...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 574 - Winning Candidate

LeetCode Problem 574 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 574 - Winning Candidate Problem Understanding This problem provides two database tables, Candidate and Vote , and asks us to determine which candidate won the election. The Candidate table stores information about each candidate. Every candidate has a unique integer id and a corresponding name . The Vote table stores the voting results. Each row represents a single vote, and...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1350 - Students With Invalid Departments

LeetCode Problem 1350 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify students who are enrolled in university departments that no longer exist in the department registry. We are given two database tables. The Departments table stores valid university departments, where each department has a unique id and a name . The Students table stores student records, where each student has a unique id ,...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1179 - Reformat Department Table

LeetCode Problem 1179 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to take a table Department that records revenue per department per month in a vertical format and convert it into a horizontal format, often called a "pivot" table. In the input, each row contains a department id , a revenue value, and a month . The primary key ensures there is at most one...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1645 - Hopper Company Queries II

LeetCode Problem 1645 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to calculate, for every month in the year 2020, the percentage of drivers who actually worked during that month. The database contains three tables: Drivers stores when each driver joined Hopper. Rides stores all ride requests. AcceptedRides stores only rides that were accepted and completed by a driver. The key observation is that a driver...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1107 - New Users Daily Count

LeetCode Problem 1107 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding We are given a database table called Traffic that records different user activities on different dates. Each row contains a user_id , an activity type, and an activity_date . A user may appear multiple times on the same day because they can perform different activities such as login , logout , homepage , jobs , or groups . The...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1809 - Ad-Free Sessions

LeetCode Problem 1809 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to identify all playback sessions during which no advertisements were shown. We are given two tables: Playback and Ads . The Playback table lists sessions for each customer, with the start and end times of each session. Each session is guaranteed to be non-overlapping for the same customer. The Ads table lists the ads...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1623 - All Valid Triplets That Can Represent a Country

LeetCode Problem 1623 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to generate all valid triplets of students representing a country from three schools: SchoolA , SchoolB , and SchoolC . Each triplet consists of one student from each school, and the triplet is only valid if all three students have distinct names and distinct IDs. The input consists of three database tables, each representing a...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1321 - Restaurant Growth

LeetCode Problem 1321 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to compute a rolling seven day summary of restaurant revenue. The input table stores individual customer transactions. Each row represents how much a single customer spent on a specific date. The important detail is that multiple customers may visit on the same day, which means we cannot directly apply a moving average on the raw...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1767 - Find the Subtasks That Did Not Execute

LeetCode Problem 1767 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem revolves around identifying which subtasks of a task were not executed. We are given two tables: Tasks and Executed . The Tasks table lists all tasks and the number of subtasks each task is divided into, while the Executed table lists subtasks that successfully ran for a given task. The goal is to produce a table containing...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1204 - Last Person to Fit in the Bus

LeetCode Problem 1204 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem gives us a database table named Queue that represents people waiting to board a bus. Each row contains a person's ID, name, weight, and boarding order. The turn column determines the exact sequence in which people attempt to board the bus. The bus has a strict weight limit of 1000 kilograms. People board one at a time,...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1308 - Running Total for Different Genders

LeetCode Problem 1308 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem is asking us to compute cumulative scores for each gender across different days in a competition. The input is a table Scores with columns player_name , gender , day , and score_points . Each row represents a player’s score on a specific day. The primary key is the combination (gender, day) , meaning each gender has unique...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1412 - Find the Quiet Students in All Exams

LeetCode Problem 1412 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem asks us to identify students who are "quiet" across all exams they participated in. A student is considered quiet if, in every exam they took, they never achieved either the highest score or the lowest score. We are given two tables: The Student table contains student IDs and names. The Exam table records exam participation and scores....

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1077 - Project Employees III

LeetCode Problem 1077 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem asks us to find the most experienced employees in each project from two database tables, Project and Employee . The Project table contains a mapping of employee_id s to project_id s, indicating which employees work on which projects. The Employee table provides additional details for each employee, including name and experience_years . The goal is to return,...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1543 - Fix Product Name Format

LeetCode Problem 1543 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem asks us to clean and aggregate sales data from a Sales table. Each row contains a unique sale_id , a product_name , and a sale_date . Due to manual data entry errors, product_name may contain extra leading or trailing spaces and may use inconsistent letter casing. Our task is to produce a report that normalizes the product...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1667 - Fix Names in a Table

LeetCode Problem 1667 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named Users with two columns: user_id and name . The user_id column uniquely identifies each user, while the name column stores a person's name using a mixture of uppercase and lowercase English letters. The task is to normalize every name so that it follows standard capitalization rules: The first character must be uppercase...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 601 - Human Traffic of Stadium

LeetCode Problem 601 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding The problem asks us to extract all consecutive records from a Stadium table where the people count is at least 100, and the consecutive streak has a length of three or more. Each row has a unique id and a corresponding visit_date . Consecutive here refers to consecutive id values, not consecutive dates. The output should be all records...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1435 - Create a Session Bar Chart

LeetCode Problem 1435 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem provides a database table named Sessions with two columns: Column Meaning session_id Unique identifier for a session duration Length of the session in seconds We need to group sessions into predefined duration ranges, called bins, and count how many sessions fall into each bin. The required bins are: Bin Label Duration Range [0-5> 0 minutes inclusive to...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1607 - Sellers With No Sales

LeetCode Problem 1607 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to identify all sellers who did not make any sales during the year 2020 . We are given three database tables: The Customer table contains information about customers in the web store. Each customer has a unique customer_id and a customer_name . However, this table is not actually necessary for solving the problem because the...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1783 - Grand Slam Titles

LeetCode Problem 1783 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to compute how many Grand Slam tennis titles each player has won across all years recorded in the database. We are given two tables: The Players table contains information about tennis players. Each row stores a unique player_id and the corresponding player_name . The Championships table stores the winners of the four Grand Slam tournaments...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1532 - The Most Recent Three Orders

LeetCode Problem 1532 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to retrieve the three most recent orders for every customer from a database. If a customer has fewer than three orders, we should return all of their orders. We are given two tables: The Customers table contains customer information. Each customer has a unique customer_id and a corresponding name . The Orders table stores customer...

Practice › LeetCode › LeetCode 11xx ›

LeetCode 1148 - Article Views I

LeetCode Problem 1148 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to identify all authors who have viewed at least one of their own articles. The input is a database table Views that contains information about articles, their authors, the viewers, and the dates on which the articles were viewed. Each row indicates a single view event, and duplicate rows are possible, meaning the same...

Practice › LeetCode › LeetCode 13xx ›

LeetCode 1378 - Replace Employee ID With The Unique Identifier

LeetCode Problem 1378 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to combine information from two database tables and return the result in a specific format. We are given an Employees table that contains basic employee information, specifically an employee id and name . We are also given an EmployeeUNI table that maps an employee id to a unique_id . The goal is to produce a...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 595 - Big Countries

LeetCode Problem 595 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to query a database table named World and return a subset of countries that qualify as big countries . Each row in the World table represents a country and contains five columns: Column Meaning name Country name continent Continent where the country belongs area Total land area in square kilometers population Number of people living...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 586 - Customer Placing the Largest Number of Orders

LeetCode Problem 586 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Orders with two columns: Column Meaning order_number Unique identifier for an order customer_number Identifier for the customer who placed the order Each row represents a single order placed by a customer. A customer may appear multiple times because a customer can place multiple orders. The task is to determine which customer...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1587 - Bank Account Summary II

LeetCode Problem 1587 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to analyze banking transaction data and determine which users currently have a balance greater than 10000 . We are given two database tables: The Users table stores account information. Each row contains: account , the unique account number name , the user's name The Transactions table stores every transaction that affects an account. Each row...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 608 - Tree Node

LeetCode Problem 608 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem gives us a database table named Tree , where each row represents a node in a tree structure. Every node has a unique identifier id and a p_id column that stores the identifier of its parent node. The task is to classify every node into one of three categories: "Root" if the node has no parent, meaning...

Practice › LeetCode › LeetCode 05xx ›

LeetCode 550 - Game Play Analysis IV

LeetCode Problem 550 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem is asking us to calculate a retention metric from a table of player activities. Specifically, we need to determine the fraction of players who log in on the day immediately following their first login . The input is a SQL table named Activity where each row represents a single player’s login on a given date and the...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1821 - Find Customers With Positive Revenue this Year

LeetCode Problem 1821 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Customers with three columns: Column Meaning customer_id Unique identifier for a customer year The year associated with the revenue revenue Revenue value for that customer in that year The combination (customer_id, year) is guaranteed to be unique, which means a customer can appear at most once for a given year. The...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 602 - Friend Requests II: Who Has the Most Friends

LeetCode Problem 602 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us a database table named RequestAccepted , where each row represents a successfully accepted friend request between two users. Every record contains a requester_id , an accepter_id , and the date the request was accepted. The important detail is that friendship is mutual. If user 1 sends a friend request to user 2 and it is...

Practice › LeetCode › LeetCode 20xx ›

LeetCode 2004 - The Number of Seniors and Juniors to Join the Company

LeetCode Problem 2004 Difficulty: 🔴 Hard Topics: Database Solution Problem Understanding This problem requires determining how many candidates a company can hire as seniors and juniors under a fixed budget of $70000 , following a strict priority: hire as many seniors as possible first, then use the remaining budget to hire juniors. The input is a table Candidates containing employee_id (unique identifier), experience (either 'Senior' or 'Junior'), and salary (monthly...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1555 - Bank Account Summary

LeetCode Problem 1555 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem gives us two database tables, Users and Transactions , and asks us to compute the final account balance for every user after applying all recorded transactions. The Users table contains the starting credit balance for each user. Every row represents one bank account, identified by user_id . The credit column is the user's current balance before processing...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1468 - Calculate Salaries

LeetCode Problem 1468 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to compute the post tax salary for every employee in the Salaries table. However, the tax rate is not determined individually for each employee. Instead, the tax rate is determined at the company level , based on the maximum salary within that company . Each row in the input table represents an employee and contains...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1264 - Page Recommendations

LeetCode Problem 1264 Difficulty: 🟡 Medium Topics: Database Solution LeetCode 1264 - Page Recommendations Problem Understanding This problem models a small social network with two database tables. The Friendship table stores friendship relationships between users. Each row (user1_id, user2_id) means those two users are friends. Friendship is effectively bidirectional, even though each pair appears only once in the table. The Likes table stores which pages each user likes. Each row...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1501 - Countries You Can Safely Invest In

LeetCode Problem 1501 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This is a SQL database problem where we need to identify countries whose average call duration is strictly greater than the global average call duration . The database consists of three tables: The Person table stores information about people, including their unique id and phone_number . The Country table maps a country_code to a country name. The Calls table...

Practice › LeetCode › LeetCode 06xx ›

LeetCode 627 - Swap Sex of Employees

LeetCode Problem 627 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem is asking us to swap the sex values of all employees in a Salary table. Each row in the table represents an employee with four columns: id , name , sex , and salary . The sex column is an ENUM with values 'm' for male and 'f' for female. The task is to flip these values...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 181 - Employees Earning More Than Their Managers

LeetCode Problem 181 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem gives us a single database table named Employee . Each row represents one employee and contains four pieces of information: Column Meaning id Unique identifier for the employee name Employee name salary Employee salary managerId The id of that employee's manager The goal is to return the names of employees whose salary is strictly greater than the...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1596 - The Most Frequently Ordered Products for Each Customer

LeetCode Problem 1596 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding The problem requires us to find the most frequently ordered product or products for each customer from a set of three tables: Customers , Orders , and Products . Each customer_id may have multiple orders, and each order contains a product_id . The goal is to output, for each customer who has made at least one order, the product_id...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1068 - Product Sales Analysis I

LeetCode Problem 1068 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem asks us to combine information from two database tables, Sales and Product , and produce a result containing the product name, the year of the sale, and the sale price for every sale record. The Sales table stores transactional information. Each row represents a product sale in a specific year. The table contains: sale_id , the identifier...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1843 - Suspicious Bank Accounts

LeetCode Problem 1843 Difficulty: 🟡 Medium Topics: Database Solution Problem Understanding This problem asks us to identify bank accounts whose monthly income exceeds a predefined limit for at least two consecutive months. We are given two tables: The Accounts table stores the maximum allowed monthly income for each account. Every account has exactly one max_income value. The Transactions table stores individual banking transactions. Each transaction belongs to an account and...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1421 - NPV Queries

LeetCode Problem 1421 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem presents two database tables: NPV and Queries . The NPV table contains historical net present value (NPV) data for different inventory items identified by an id and a year . The Queries table contains requests for the NPV of specific inventory items at specific years. Each row in Queries represents a single query. The task is to...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 197 - Rising Temperature

LeetCode Problem 197 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding The problem gives us a database table named Weather that stores daily temperature records. Each row contains three fields: a unique id , a recordDate , and the temperature recorded on that date. The task is to find all rows where the temperature is higher than the temperature recorded on the previous calendar day. In other words, for each...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 196 - Delete Duplicate Emails

LeetCode Problem 196 Difficulty: 🟢 Easy Topics: Database Solution Problem Understanding This problem provides a database table named Person with two columns: id int email varchar The id column is unique because it is the primary key. The email column may contain duplicate values, meaning multiple rows can share the same email address. The task is to delete duplicate email rows while keeping exactly one row for each unique email...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1084: Sales Analysis III

Problem Restatement Using Sales(sale_id, product_id, buyer_id, sale_date, quantity, price) and Product(product_id, product_name, unit_price) , report products that were sold only between 2019-01-01 and 2019-03-31 (Q1 2019). Edge Cases Match the aggregate to the question: use raw COUNT or SUM for rows/amounts, and COUNT(DISTINCT ...) only for unique entities. Tie cases should return every qualifying row unless the statement asks for a single row. For outer joins, keep filters on the...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1068: Product Sales Analysis I

Problem Restatement We have two tables: Sales(sale_id, product_id, year, quantity, price) — each row is a sale. Product(product_id, product_name) — product information. We need to return product_name , year , and price for each sale. Input and Output Table Schema Sales sale_id INT , product_id INT , year INT , quantity INT , price INT Product product_id INT , product_name VARCHAR Return a table with product_name , year , price...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1083: Sales Analysis II

Problem Restatement We have Sales(seller_id, product_id, buyer_id, sale_date, quantity, price) and Product(product_id, product_name, unit_price) . Find buyers who bought the product 'S8' but not the product 'iPhone' . Edge Cases Match the aggregate to the question: use raw COUNT or SUM for rows/amounts, and COUNT(DISTINCT ...) only for unique entities. Tie cases should return every qualifying row unless the statement asks for a single row. For outer joins, keep filters...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1069: Product Sales Analysis II

Problem Restatement Using the Sales(sale_id, product_id, year, quantity, price) table, report the total quantity sold for each product. Input and Output Table Schema Sales sale_id INT , product_id INT , year INT , quantity INT , price INT Return a table with product_id and total_quantity . Edge Cases Match the aggregate to the question: use raw COUNT or SUM for rows/amounts, and COUNT(DISTINCT ...) only for unique entities. Tie cases...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1070: Product Sales Analysis III

Problem Restatement Using the Sales(sale_id, product_id, year, quantity, price) table, find the product_id , first_year , quantity , and price of the first-year sale for each product. The first year is the earliest year for each product_id . Input and Output Table Schema Sales sale_id INT , product_id INT , year INT , quantity INT , price INT Return product_id , first_year , quantity , price for each product's first...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1076: Project Employees II

Problem Restatement Using the Project(project_id, employee_id) table, report the project(s) with the most employees. Edge Cases Match the aggregate to the question: use raw COUNT or SUM for rows/amounts, and COUNT(DISTINCT ...) only for unique entities. Tie cases should return every qualifying row unless the statement asks for a single row. For outer joins, keep filters on the joined table in the ON clause when unmatched rows must remain visible....

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1082: Sales Analysis I

Problem Restatement We have a Sales(seller_id, product_id, buyer_id, sale_date, quantity, price) table. Report the seller(s) with the highest total sale price. Edge Cases Match the aggregate to the question: use raw COUNT or SUM for rows/amounts, and COUNT(DISTINCT ...) only for unique entities. Tie cases should return every qualifying row unless the statement asks for a single row. For outer joins, keep filters on the joined table in the ON...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1097: Game Play Analysis V

Problem Restatement We have an Activity(player_id, device_id, event_date, games_played) table. For each first login date, compute the fraction of players who logged in again the very next day. Return the result rounded to 2 decimal places. Edge Cases Match the aggregate to the question: use raw COUNT or SUM for rows/amounts, and COUNT(DISTINCT ...) only for unique entities. Tie cases should return every qualifying row unless the statement asks for...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1098: Unpopular Books

Problem Restatement We have Books(book_id, name, available_from) and Orders(order_id, book_id, quantity, dispatch_date) tables. Report books that have been available for more than 1 month (available before 2019-01-01) and sold fewer than 10 copies in the last year (between 2018-06-23 and 2019-06-23). Edge Cases Match the aggregate to the question: use raw COUNT or SUM for rows/amounts, and COUNT(DISTINCT ...) only for unique entities. Tie cases should return every qualifying row...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1077: Project Employees III

Problem Restatement Using Project(project_id, employee_id) and Employee(employee_id, name, experience_years) , find the most experienced employee for each project. If there are ties, return all tied employees. Edge Cases Match the aggregate to the question: use raw COUNT or SUM for rows/amounts, and COUNT(DISTINCT ...) only for unique entities. Tie cases should return every qualifying row unless the statement asks for a single row. For outer joins, keep filters on the...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1050: Actors and Directors Who Cooperated At Least Three Times

Problem Restatement We have a table ActorDirector(actor_id, director_id, timestamp) . We need to return all (actor_id, director_id) pairs where the actor has cooperated with the director at least three times. Input and Output Table Schema ActorDirector actor_id INT , director_id INT , timestamp INT Return a table with actor_id and director_id . Examples ActorDirector: +----------+-------------+----------+ | actor_id | director_id | timestamp | +----------+-------------+----------+ | 1 | 1 | 0 |...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1075: Project Employees I

Problem Restatement We have two tables: Project(project_id, employee_id) — maps employees to projects. Employee(employee_id, name, experience_years) — employee details. We need to report the average experience years for each project, rounded to 2 decimal places. Edge Cases Match the aggregate to the question: use raw COUNT or SUM for rows/amounts, and COUNT(DISTINCT ...) only for unique entities. Tie cases should return every qualifying row unless the statement asks for a...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1045: Customers Who Bought All Products

Problem Restatement We have two tables: Customer(customer_id, product_key) — records each purchase. Product(product_key) — all products in the catalog. We need to return the customer_id of customers who bought all products in the catalog. Input and Output Table Schema Customer customer_id INT , product_key INT Product product_key INT Return a table with one column: customer_id . Examples Customer: Product: +-------------+----------+ +-------------+ | customer_id | product_key | | product_key | +-------------+----------+...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 197: Rising Temperature

Problem Restatement We are given a table named Weather . Schema: Column Type id int recordDate date temperature int The id column is unique. There are no duplicate recordDate values. We need to find the id of every date where the temperature is higher than the temperature on the previous day. Example table: id recordDate temperature 1 2015-01-01 10 2 2015-01-02 25 3 2015-01-03 20 4 2015-01-04 30 Expected output:...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 175: Combine Two Tables

Problem Restatement We are given two tables: Person and Address . The Person table stores each person's ID, first name, and last name. The Address table stores address records. Each address belongs to a person through personId . We need to report this information for every person: firstName, lastName, city, state The important part is that every person must appear in the result, even if that person has no address....

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 615: Average Salary: Departments VS Company

Problem Restatement We are given two tables: Salary and Employee . The Salary table stores each employee's salary for a month. Column Type Meaning id int Salary record id employee_id int Employee id amount int Salary amount pay_date date Salary payment date The Employee table stores each employee's department. Column Type Meaning employee_id int Employee id department_id int Department id We need to compare each department's average salary with the...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 614: Second Degree Follower

Problem Restatement We are given a table called Follow . Each row means one user follows another user. Column Type Meaning followee varchar The user being followed follower varchar The user who follows followee The pair (followee, follower) is the primary key. A second-degree follower is a user who: follows at least one user is followed by at least one user We need to return every second-degree follower and the...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 613: Shortest Distance in a Line

Problem Restatement We are given a table called Point . Each row stores one point on the X-axis. Column Type Meaning x int Position of the point on the X-axis The column x is the primary key, so every point is unique. We need to find the shortest distance between any two points. The official problem asks for the minimum distance between any two points from the Point table. Input...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 612: Shortest Distance in a Plane

Problem Restatement We are given a table called Point2D . Each row represents one point in a 2D plane. Column Type Meaning x decimal x-coordinate y decimal y-coordinate We need to find the shortest Euclidean distance between any two distinct points. The result should contain one column: Column Meaning shortest Minimum distance between any pair of points The final answer should be rounded to two decimal places. The official problem...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 610: Triangle Judgement

Problem Restatement We are given a table called Triangle . Each row contains three integer side lengths: Column Type Meaning x int First side length y int Second side length z int Third side length For each row, we need to report whether the three side lengths can form a valid triangle. The result should contain the original side lengths and a new column called triangle , whose value is...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 550: Game Play Analysis IV

Problem Restatement We are given a table named Activity . Each row records one player's login activity on one date. We need to report the fraction of players who logged in again on the day immediately after their first login date. The final answer must be rounded to 2 decimal places. The result has one column: fraction The task is to count players with day-two retention, then divide by the...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 608: Tree Node

Problem Restatement We are given a table called Tree . Each row represents one node in a binary tree. Column Type Meaning id int Node id p_id int Parent node id We need to classify every node into one of three types: Type Meaning Root The node has no parent Leaf The node has no children Inner The node has both a parent and at least one child The result...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 574: Winning Candidate

Problem Restatement We are given two tables. Candidate : Column Type Meaning id int Candidate id name varchar Candidate name Vote : Column Type Meaning id int Vote id candidateId int The candidate who received this vote We need to report the name of the candidate who received the largest number of votes. The test cases guarantee exactly one winner. The result table can be returned in any order because...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 607: Sales Person

Problem Restatement We are given three tables: SalesPerson , Company , and Orders . The SalesPerson table stores salesperson information. Column Type Meaning sales_id int Salesperson id name varchar Salesperson name salary int Salary commission_rate int Commission rate hire_date date Hire date The Company table stores company information. Column Type Meaning com_id int Company id name varchar Company name city varchar Company city The Orders table stores order information. Column...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 571: Find Median Given Frequency of Numbers

Problem Restatement We are given a Numbers table. Column Type Meaning num int The number value frequency int How many times this number appears Each row stores a number and its frequency. Conceptually, the table represents a decompressed list of numbers. For example, if num = 0 and frequency = 7 , then 0 appears seven times in the full list. We need to report the median of all numbers...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 570: Managers with at Least 5 Direct Reports

Problem Restatement We are given an Employee table. Column Type Meaning id int Employee id name varchar Employee name department varchar Department name managerId int Id of this employee's manager If managerId is NULL , the employee does not report to anyone. We need to find managers who have at least five direct reports. A direct report means an employee whose managerId is equal to that manager's id . Return...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 569: Median Employee Salary

Problem Restatement We are given an Employee table. Column Type Meaning id int Employee id company varchar Company name salary int Employee salary We need to return the rows that contain the median salary of each company. When sorting salaries inside a company, ties are broken by id . If a company has an odd number of employees, return the one middle row. If a company has an even number...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 512: Game Play Analysis II

Problem Restatement We are given an Activity table. Each row records one player login on one date, including the device used and the number of games played. We need to report the device that each player used on their first login date. The result can be returned in any order. The table has columns player_id , device_id , event_date , and games_played ; (player_id, event_date) is the primary key. The...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 511: Game Play Analysis I

Problem Restatement We are given an Activity table. Each row records one player login on one date, together with the device used and the number of games played. We need to report the first login date for each player. The result can be returned in any order. The table has columns player_id , device_id , event_date , and games_played , and the goal is to find the earliest event_date for...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 603: Consecutive Available Seats

Problem Restatement We are given a table called Cinema . Each row tells us whether a seat is free or occupied. Column Type Meaning seat_id int Seat id free bool 1 means free, 0 means occupied We need to return all free seats that are part of at least one consecutive pair of free seats. The result should be ordered by seat_id . The problem note says seat_id is auto-incremented,...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 602: Friend Requests II: Who Has the Most Friends

Problem Restatement We are given a table called RequestAccepted . Each row means one friend request was accepted. Column Type Meaning requester_id int The user who sent the friend request accepter_id int The user who accepted the friend request accept_date date The date when the request was accepted We need to find the user who has the most friends and return: Column Meaning id The user id num The number...

Practice › LeetCode › LeetCode (archived) › LeetCode 06xx ›

LeetCode 601: Human Traffic of Stadium

Problem Restatement We are given a table called Stadium . Each row records one stadium visit day. The table has three columns: Column Type Meaning id int Visit id visit_date date Date of the visit people int Number of people who visited We need to return all rows that are part of a group of at least three consecutive id values where every row has people >= 100 . The...

Practice › LeetCode › LeetCode (archived) › LeetCode 05xx ›

LeetCode 534: Game Play Analysis III

Problem Restatement We are given a table named Activity . Each row records one player's activity on one date. It contains the player id, device id, event date, and number of games played. We need to report, for each player and each date, the total number of games the player has played so far up to that date. The output should contain: player_id event_date games_played_so_far The result may be returned...

Practice › LeetCode › LeetCode (archived) › LeetCode 02xx ›

LeetCode 262: Trips and Users

Problem Restatement We are given two tables: Trips and Users . Trips stores taxi trip requests. Users stores user information, including whether a user is banned. We need to find the cancellation rate for each day from: '2013-10-01' to: '2013-10-03' Only trips where both the client and driver are unbanned should be counted. The cancellation rate is: cancelled requests / total requests Cancelled means the trip status is either: 'cancelled_by_driver'...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 185: Department Top Three Salaries

Problem Restatement We are given two tables: Employee and Department . Employee stores employee information. Column Type id int name varchar salary int departmentId int Department stores department information. Column Type id int name varchar Each employee belongs to a department through Employee.departmentId . We need to find employees who are high earners in their department. A high earner is an employee whose salary is in the top three unique...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 184: Department Highest Salary

Problem Restatement We are given two tables: Employee and Department . Employee stores employee information. Column Type id int name varchar salary int departmentId int Department stores department information. Column Type id int name varchar Each employee belongs to one department through Employee.departmentId . We need to find employees who have the highest salary in each department. If multiple employees share the highest salary in the same department, we return...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 183: Customers Who Never Order

Problem Restatement We are given two tables: Customers and Orders . Customers stores customer information. Column Type id int name varchar Orders stores order information. Column Type id int customerId int The customerId column in Orders refers to Customers.id . We need to find all customers who never placed an order. The result can be returned in any order. The official problem asks for all customers who never order anything....

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 182: Duplicate Emails

Problem Restatement We are given a table named Person . Column Type id int email varchar The id column is the primary key. Each row stores one email address. The email field is guaranteed to be non-null. We need to report all duplicate emails. A duplicate email means an email value that appears more than once in the table. The result can be returned in any order. The official statement...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 181: Employees Earning More Than Their Managers

Problem Restatement We are given a table named Employee . Column Type id int name varchar salary int managerId int Each row stores one employee. The managerId column points to the id of that employee's manager. We need to return the names of employees who earn more than their managers. The result can be returned in any order. The official problem asks for employees whose salary is greater than their...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 180: Consecutive Numbers

Problem Restatement We are given a table named Logs . Column Type id int num varchar The column id is the primary key. It is an auto-increment column starting from 1 . We need to find every number that appears at least three times consecutively. The result can be returned in any order. The output column should be named ConsecutiveNums . The official statement asks for all numbers that appear...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 178: Rank Scores

Problem Restatement We are given a table named Scores . Column Type id int score decimal Each row stores the score of a game. We need to rank all scores from highest to lowest. The ranking rules are: Rule Meaning Higher score gets smaller rank The highest score has rank 1 Equal scores share the same rank Two 4.00 scores both get rank 1 No rank gaps After rank 1...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 177: Nth Highest Salary

Problem Restatement We are given a table named Employee . Column Type id int salary int Each row stores one employee and that employee's salary. We need to write a SQL function that returns the n th highest distinct salary. If there are fewer than n distinct salaries, the function should return null . The official problem asks for the n th highest distinct salary from Employee , returning null...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 176: Second Highest Salary

Problem Restatement We are given a table named Employee . Column Type id int salary int Each row stores one employee and their salary. We need to return the second highest distinct salary. The word distinct matters. If two employees both have salary 300 , that salary still counts as one salary level. If there is no second highest distinct salary, we return null . Input and Output Item Meaning...

Wiki › Algorithms › 02. Data Structures › 3. Specialized, Persistent, Concurrent, and External Structures ›

3.6 External-Memory and Database Structures

3.6 External-memory and database structures, 35 index slug name 1 external-memory-structure External Memory Structure 2 block-model Block Model 3 buffer-pool Buffer Pool 4 page-cache Page Cache 5 slotted-page Slotted Page 6 heap-file Heap File 7 sorted-file Sorted File 8 clustered-index Clustered Index 9 secondary-index Secondary Index 10 b-tree-index B Tree Index 11 b-plus-tree-index B Plus Tree Index 12 lsm-tree LSM Tree 13 memtable Memtable 14 sstable SSTable 15 bloom-filter-index Bloom...

Wiki › Algorithms › 01. Searching and Sorting › 10. External Memory, Cache, and Database Sorting ›

TPMMS

Two Phase Multiway Merge Sort Two Phase Multiway Merge Sort (TPMMS) is a practical external sorting algorithm used in database systems. It assumes that all sorted runs can be merged in a single pass using available memory buffers. The method minimizes the number of disk passes, which dominates cost in external memory settings. Model Let: $N$ = total number of elements $M$ = memory capacity $B$ = block size Memory...

Wiki › Algorithms › 01. Searching and Sorting › 10. External Memory, Cache, and Database Sorting ›

Sort Merge Join Sort Phase

Sort Merge Join Sort Phase The sort phase of sort-merge join orders each input relation by the join key before the merge phase begins. If an input is already ordered by a suitable index or previous query operator, the database can skip sorting that input. This phase is important because the merge join itself requires ordered streams. Without sorted inputs, the join cannot advance both sides efficiently. Problem Given two...

Wiki › Algorithms › 01. Searching and Sorting › 10. External Memory, Cache, and Database Sorting ›

Spill Sort

Spill Sort Spill sort is a practical external sorting pattern used when an operator begins as an in-memory sort but exceeds its memory budget. When memory fills, the current data is sorted and spilled to temporary storage as a run. After all input has been read, the spilled runs are merged. This is common in databases, query engines, log processors, and stream processors. Problem Given an input stream and a...

Wiki › Algorithms › 01. Searching and Sorting › 10. External Memory, Cache, and Database Sorting ›

Database External Sort

Database External Sort Database external sort is the disk-based sorting procedure used inside relational database query engines. It appears in query plans for operations such as ORDER BY , GROUP BY , DISTINCT , window functions, and sort-merge joins. The method is usually a variant of external merge sort with database-specific concerns: rows, tuple comparison, memory quotas, spill files, collation rules, NULL ordering, and stable execution under limited working memory....

#database

LeetCode 3421 - Find Students Who Improved

LeetCode 3601 - Find Drivers with Improved Fuel Efficiency

LeetCode 3611 - Find Overbooked Employees

LeetCode 3564 - Seasonal Sales Analysis

LeetCode 3521 - Find Product Recommendation Pairs

LeetCode 3482 - Analyze Organization Hierarchy

LeetCode 3401 - Find Circular Gift Exchange Chains

LeetCode 3415 - Find Products with Three Consecutive Digits

LeetCode 3586 - Find COVID Recovery Patients

LeetCode 3580 - Find Consistently Improving Employees

LeetCode 3570 - Find Books with No Available Copies

LeetCode 3554 - Find Category Recommendation Pairs

LeetCode 3497 - Analyze Subscription Conversion

LeetCode 3475 - DNA Pattern Recognition

LeetCode 3465 - Find Products with Valid Serial Numbers

LeetCode 3451 - Find Invalid IP Addresses

LeetCode 3436 - Find Valid Emails

LeetCode 3390 - Longest Team Pass Streak

LeetCode 3188 - Find Top Scoring Students II

LeetCode 1867 - Orders With Maximum Quantity Above Average

LeetCode 2377 - Sort the Olympic Table

LeetCode 2837 - Total Traveled Distance

LeetCode 3236 - CEO Subordinate Hierarchy

LeetCode 3246 - Premier League Table Ranking

LeetCode 2504 - Concatenate the Name and the Profession

LeetCode 2112 - The Airport With the Most Traffic

LeetCode 2173 - Longest Winning Streak

LeetCode 2687 - Bikes Last Time Used

LeetCode 2994 - Friday Purchases II

LeetCode 2199 - Finding the Topic of Each Post

LeetCode 2082 - The Number of Rich Customers

LeetCode 2298 - Tasks Count in the Weekend

LeetCode 2922 - Market Analysis III

LeetCode 2978 - Symmetric Coordinates

LeetCode 2329 - Product Sales Analysis V

LeetCode 2175 - The Change in Global Rankings

LeetCode 2159 - Order Two Columns Independently

LeetCode 2324 - Product Sales Analysis IV

LeetCode 3087 - Find Trending Hashtags

LeetCode 3308 - Find Top Performing Driver

LeetCode 2480 - Form a Chemical Bond

LeetCode 3103 - Find Trending Hashtags II

LeetCode 1907 - Count Salary Categories

LeetCode 3252 - Premier League Table Ranking II

LeetCode 1972 - First and Last Call On the Same Day

LeetCode 2986 - Find Third Transaction

LeetCode 3220 - Odd and Even Transactions

LeetCode 2688 - Find Active Users

LeetCode 3293 - Calculate Product Final Price

LeetCode 3268 - Find Overlapping Shifts II

LeetCode 2072 - The Winner University

LeetCode 2362 - Generate the Invoice

LeetCode 2252 - Dynamic Pivoting of a Table

LeetCode 2669 - Count Artist Occurrences On Spotify Ranking List

LeetCode 2346 - Compute the Rank as a Percentage

LeetCode 2853 - Highest Salaries Difference

LeetCode 2738 - Count Occurrences in Text

LeetCode 3051 - Find Candidates for Data Scientist Position

LeetCode 3358 - Books with NULL Ratings

LeetCode 2984 - Find Peak Calling Hours for Each City

LeetCode 2991 - Top Three Wineries

LeetCode 1892 - Page Recommendations II

LeetCode 3328 - Find Cities in Each State II

LeetCode 3057 - Employees Project Allocation

LeetCode 2989 - Class Performance

LeetCode 2474 - Customers With Strictly Increasing Purchases

LeetCode 2118 - Build the Equation

LeetCode 2990 - Loan Types

LeetCode 1990 - Count the Number of Experiments

LeetCode 3374 - First Letter Capitalization II

LeetCode 2314 - The First Day of the Maximum Recorded Degree in Each City

LeetCode 3126 - Server Utilization Time

LeetCode 2686 - Immediate Food Delivery III

LeetCode 1853 - Convert Date Format

LeetCode 2701 - Consecutive Transactions with Increasing Amounts

LeetCode 1919 - Leetcodify Similar Friends

LeetCode 2356 - Number of Unique Subjects Taught by Each Teacher

LeetCode 2720 - Popularity Percentage

LeetCode 2854 - Rolling Average Steps