sql语句查询结果合并union all用法_数据库技巧

--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