--MySql，分页
--select * from biaoming where tiaojian limit num1（start）,num2(size)
----
select ename,rownum from emp;
select ename,rownum from (select * from emp);
----三层过滤，效率较高
select t2.* from (select t1.*, rownum rn from (select * from emp)t1 where rownum<=6)t2 where rn>=4;
--第一层：
--select * from emp ..
--第二层：
--select * from (第一层) where rownum <=6(endNum);
--第三层：
--select * from (第二层) where rownum >=4(startNum);
--按照入职时间的顺序，查询从第7个到第10个人
select t2.* from (select t1.*, rownum rn from (select * from emp order by hiredate)t1 where rownum<=10)t2 where rn>=7;
---------------合并查询
------union
------union all
------intersect