思路：
1.找到每个project的最大积累年数
2.找到相等的行并记录

sql

# Write your MySQL query statement below
select t1.project_id, t1.employee_id
from 
(
    # 找到每个p和e的关系
    select p.project_id, p.employee_id, e.experience_years
    from Project p, Employee e
    where p.employee_id = e.employee_id

) t1,
(
    # 找到每个project最大的时间
    select p.project_id, max(experience_years) as max_years
    from Project p, Employee e
    where p.employee_id = e.employee_id
    group by p.project_id
) t2
where t1.project_id = t2.project_id
and t1.experience_years = t2.max_years

总结：
先找max再找和max相同的记录