sql语句查询结果合并union 和union all用法

核心提示：--合并重复行select * from Aunion select * from B--不合并重复行select * from Aunion allselect * from B按某个字段排序--合并重复行select *from (select * from Aunion select * from B) AS T

--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(WINDOWS平台上强大的数据库平台)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(和PHP搭配之最佳组合)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。