11 子查询

select name from department where  id in
(select dep_id from employee 
group by dep_id
having avg(age)>25)
;

#查询技术部门员工的姓名

select name from employee where dep_id=(
select id from department where name='技术'
)
;

#查询不足1人的部门名

select name from department where id not in (
select distinct dep_id from employee
）;

#查询大于所有人平均年龄的员工名与年龄

select name, age from employee where age> (
select avg(age) from employee);

#带EXISTS关键字的子查询

select * from employee
where EXISTS
(select id from department where name='IT');

#查询每个部门最新入职的员工

select * from employee as t1
inner join
(select post, max(hire_date) as max_hire_date from employee 
group by post) as t2
on t1.post = t2.post
where t1.hire_date =t2.max_hire_date
;