sql语句查询结果合并union 和union all用法

最新推荐文章于 2023-02-01 16:44:36 发布

转载最新推荐文章于 2023-02-01 16:44:36 发布 · 899 阅读

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本文介绍了SQL中Union与Union All的区别及用法，并通过具体示例展示了如何使用这两种方式来合并不同的查询结果，包括如何按特定字段排序。

--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：http://www.qudong.com/soft/program/Sql%20Server/jiqiaoyunyong/20080318/1840.html