oracle集合查询

并集
Select  * from emp where deptno=10 union select * from emp where deptno=20;
Select  * from emp where deptno=10 union all select * from emp where deptno=20;
Select * from emp where ename like ‘%A%’ or ename like ‘%M%’;
Select * from emp where ename like ‘%A%’ union ename like ‘%M%’;//去掉共有部分
Select * from emp where ename like ‘%A%’ union all ename like ‘%M%’;//不去掉
交集
Select * from emp where ename like ‘%A%’ intersect  ename like ‘%M%’;//共有的部分
差集
属于第一不属于第二
Order  by 字句只能出现在最后一个语句上，第一个select语句接受的列 名称或者别名
查询结果的列名 必须与第一个select的列名一致
Select * from (select * from emp where sal between 700 and 1300 union select * from emp where sal between 1200 and 1400) order by sal desc;
select  ename,sal from emp where sal between 700 adn 1300 union select ename,sal from emp where sal between 1200 and 1400 order by sal deces;
select语句中参数类型和个数要一致
可以使用括号改变集合执行的顺序
集合运算采用第一个语句的表头作为表头


摘自：http://www.2cto.com/database/201203/123130.html