1、UNION取得两个结果集的并集并去掉重复行 AUB

SELECT ename,job,sal FROM emp WHERE sal>2500 UNION

SELECT ename,job,sal FROM emp WHERE job='MANAGER' ORDER BY 1;

等同于

SELECT ename,job,sal FROM emp WHERE sal>2500 OR job='MANAGER' ORDER BY 1;

UNION ALL取得两个结果集的并集并不去掉重复行

SELECT ename,job,sal FROM emp WHERE sal>2500 UNION ALL

SELECT ename,job,sal FROM emp WHERE job='MANAGER' ORDER BY 1;

2、INTERSECT取得两个结果集的交集 A交B

SELECT ename,job,sal FROM emp WHERE sal>2500 INTERSECT

SELECT ename,job,sal FROM emp WHERE job='MANAGER' ORDER BY 1;

等同于

SELECT ename,job,sal FROM emp WHERE sal>2500 AND job='MANAGER' ORDER BY 1;

3、MINUS取得两个集合的差集，只显示在集合A中的数据，并且不属于集合B的数据

SELECT ename,job,sal FROM emp WHERE sal>2500 MINUS

SELECT ename,job,sal FROM emp WHERE job='MANAGER' ORDER BY 1;

4、