sql 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