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主题： sql语句查询结果合并union 和union all用法

nini

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2015-9-17 17:18:38 | [全部帖] [楼主帖]

楼主

--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

在DB2里使用union时一定要注意相对应的字段一定是数据类型一样，输出时可以任意显示的列，但不能输出不同类型或不同表结构。因为这样会出错。

--转自