ORACLE SQL 集合操作

第十五章:集合操作
create table emp_tmp as select * from emp where deptno=10;
insert into emp_tmp values (7935,'alvin','clerk',7566,sysdate,777,null,40);

select empno,ename,deptno from emp;
select empno,ename,deptno from emp_tmp;

并集：
--union 有去重操作
select empno,ename,deptno from emp
union
select empno,ename,deptno from emp_tmp;

--union all 不去重
select empno,ename,deptno from emp
union all
select empno,ename,deptno from emp_tmp;

交集:intersect
select empno,ename,deptno from emp
intersect
select empno,ename,deptno from emp_tmp;

差集:minus
select empno,ename,deptno from emp
minus
select empno,ename,deptno from emp_tmp;

select empno,ename,deptno from emp_tmp
minus
select empno,ename,deptno from emp;

两个查询所枚举的列的数量不同:
select empno,ename,sal from emp
union
select deptno,dname,null from dept;