SQL练习 2022/7/3

184. 部门工资最高的员工

题干

代码思路

1. 嵌套查询，先查部门的最高工资，然后联合表再查人

select 
    department.name as Department,
    employee.name as Employee,
    employee.salary as Salary
from 
    employee left join department 
on 
    department.id=employee.departmentId
where 
    (departmentId,salary) in 
    (select 
        departmentId ,max(salary)
    from employee
    group by departmentId)

2. 开窗函数
   利用dense_rank() over()函数根据部门分区得出排名

select
     Department,Employee,salary
from
    (select
     d.name Department , e.name Employee,e.salary,dense_rank() over(partition by departmentId order by salary desc)rn
    from Employee e,Department d
     where e.departmentId = d.id)
where rn=1

196. 删除重复的电子邮箱

题干
代码思路

1. 简单查询

delete p1.*
from person p1,person p2
where p1.email=p2.email and p1.id>p2.id

delete from person
where person.id in
(
    select id
    from
        (select p1.id
        from person p1,person p2
        where p1.email=p2.email and p1.id>p2.id)a
)