# 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 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 p.project_id,
       ROUND(AVG(e.experience_years), 2) AS average_years
FROM Project p
JOIN Employee e ON p.employee_id = e.employee_id
GROUP BY p.project_id;
```

## Code Explanation

Join `Project` with `Employee` on `employee_id` to get experience years for each project member.

`GROUP BY project_id` groups each project's employees.

`AVG(experience_years)` computes the average, and `ROUND(..., 2)` formats to 2 decimal places.