select * from teacher
--联合查询
--01.union (并集)
select tno from teacher where tno>1080 union
(select tno from teacher where tno>1090)
--02.union all(并集并且显示重复的数据)
select tno from teacher where tno>1080 union all
(select tno from teacher where tno>1090)
--03.minus(补集) a minus b a-b相当于去掉重复的数据 确保a的返回大于b的范围
select tno from teacher where tno>1080 minus
(select tno from teacher where tno>1090)
--04.intersect(交集) 只查询重复的数据
select tno from teacher where tno>1080 intersect
(select tno from teacher where tno>1090)
（以上内容来自王硕老师）