mysql学习之exists

exists

语法：exists（完整的查询语句）
结果：
1或者0

select exists(select department_id from employees);

select exists(select department_id from employees where salary='400000');

查询有员工的部门名称

select department_name
from departments d
where exists(select * from employees e where d.department_id = e.department_id);

可以使用in进行替换

select department_name
from departments d
where d.department_id in (select department_id from employees);