sql语句查询结果合并union all用法

大概的思想是用union 和union all

--合并重复行
select * from A
union
select * from B


--不合并重复行
select * from A
union all
select * from B


按某个字段排序
--合并重复行
select *
from (
select * from A
union
select * from B) AS T
order by 字段名

--不合并重复行
select *
from (
select * from A
union all
select * from B) AS T
order by 字段名

//sql server版
Select * From (
select top 2 id,adddate,title,url from bArticle where ClassId='1' order by adddate desc) A
Union All
Select * From (
select top 2 id,adddate,title,url from bArticle where ClassId='2' order by adddate desc) B
Union All
Select * From (
select top 2 id,adddate,title,url from bArticle where ClassId='3' order by adddate desc) C
Union All
Select * From (
select top 2 id,adddate,title,url from bArticle where ClassId='4' order by adddate desc) D


//mysql版
Select * From (
select id,adddate,title,url from bArticle where ClassId='1' order by adddate desc limit 0,2) A
Union All
Select * From (
select id,adddate,title,url from bArticle where ClassId='2' order by adddate desc limit 0,2) B
Union All
Select * From (
select id,adddate,title,url from bArticle where ClassId='3' order by adddate desc limit 0,2) C
Union All
Select * From (
select id,adddate,title,url from bArticle where ClassId='4' order by adddate desc limit 0,2) D