关键字--exists用法

1. exists后面跟一个布尔值

   SELECT * FROM EMP EXISTS (SELECT * FROM DEPT WHERE DEPTNO = 10);SELECT * FROM EMP EXISTS (SELECT * FROM DEPT WHERE DEPTNO = 50);

2. 查询子查询中外键有记录的数据

   a.查询出DEPT表中有人的部门    SELECT * FROM DEPT D EXISTS (SELECT * FROM EMP E WHERE E.DEPTNO = D.DEPTNO);    或    SELECT * FROM DEPT WHERE DEPTNO IN (SELECT DEPTNO FROM EMP);b.把EMP表中最低工资的人去掉    SELECT * FROM EMP E1 EXISTS (SELECT * FROM EMP E2 WHERE E1.SAL>E2.SAL);