# 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 joined table in the `ON` clause when unmatched rows must remain visible.

## Common Pitfalls

- Do not put aggregate filters in `WHERE`; use `HAVING` after `GROUP BY`.
- When the answer needs all tied winners, avoid `LIMIT 1` unless the statement explicitly asks for one row.

## Implementation

```sql
SELECT s.product_id, p.product_name
FROM Sales s
JOIN Product p ON s.product_id = p.product_id
GROUP BY s.product_id, p.product_name
HAVING MIN(s.sale_date) >= '2019-01-01'
   AND MAX(s.sale_date) <= '2019-03-31';
```

## Code Explanation

Group by `product_id` to get all sales for each product.

`MIN(sale_date) >= '2019-01-01'` ensures no sale before Q1 2019.

`MAX(sale_date) <= '2019-03-31'` ensures no sale after Q1 2019.

Together, these conditions confirm all sales for the product are within Q1 2019.