FOR YOU

exists ​- 말그대로 존재하는지 안하는지 알아보는 연산자 in 이랑 역할은 비슷하지만 좀다름. ​ ex) in을 쓸 경우 select department_id, employee_id from employees where department_id in (30,60,90)​ ​ ex2) exists를 쓸 경우 select emp.department_id, emp.employee_id from employees emp where exists (select dep.department_id from departments dep where dep.department_id in (30, 60, 90) and emp.department_id=dep.department_id) 1)exists 는 뒤에 서브쿼리만 올..