Union
例如：
查看职位是manager的员工以及薪水大于2500的员工？
SELECT ename, job, sal?
? ? From emp
? ? Where job = 'MANAGER'
UNION all
SELECT ename, job, sal
? ? From emp
? ? Where sal > 2500
;
SELECT ename, job, sal?
? ? From emp
? ? Where job = 'MANAGER'
UNION
SELECT ename, job, sal
? ? From emp
? ? Where sal > 2500
;。
