select name from department where id in (select dep_id from employee group by dep_id having avg(age)>25) ;
# Name Query technology department staff
select name from employee where dep_id=( select id from department where name='技术' ) ;
# Inquiry less than 1 person department name
select name from department where id not in ( select distinct dep_id from employee );
# Query is greater than the average age for all employees name and age
select name, age from employee where age> ( select avg(age) from employee);
# Subqueries with EXISTS keyword
select * from employee where EXISTS (select id from department where name='IT');
# Query each department newest recruits
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 ;