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 ;