mysql中union和union all的区别

分类：Database, MySQL 阅读 (2,034) Add comments

7月 152014

union all对于重复的数据也会提取出来

union 不会提取重复的数据

一个sql语句可以有多个union或者union all连接

如果要对连接表中的字段排序，把union的表当成一个子表来操作，如下：

select (
select id, username from a
union 
select id, qqname as username from b) as datatable order by id

select (

select id, username from a

union

select id, qqname as username from b) as datatable order by id

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