1、题目描述
Write an SQL query that reports the average experience years of all the employees for each project, rounded to 2 digits.
The query result format is in the following example:
Project table:
| project_id | employee_id |
|---|---|
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 2 | 1 |
| 2 | 4 |
Employee table:
| employee_id | name | experience_years |
|---|---|---|
| 1 | Khaled | 3 |
| 2 | Ali | 2 |
| 3 | John | 1 |
| 4 | Doe | 2 |
Result table:
| project_id | average_years |
|---|---|
| 1 | 2.00 |
| 2 | 2.50 |
The average experience years for the first project is (3 + 2 + 1) / 3 = 2.00 and for the second project is (3 + 2) / 2 = 2.50
2、解题思路
两表联查，求平均数
3、提交记录
select project_id,round(avg(experience_years),2) as average_years
from Project p left join Employee e
on p.employee_id=e.employee_id
group by project_id
