데이터 분석 21일차
https://leetcode.com/problems/project-employees-i/submissions/1580093171/


- 정답코드
select project_id , round(sum(e.experience_years)/ count(p.project_id),2 )average_years from project p left join employee e on p.employee_id = e.employee_id group by p.project_id
첫날 한일