请问一个关于php+mysql的有关问题

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Release: 2016-06-13 12:05:55
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请教一个关于php+mysql的问题
要在一个表中查询数据,条件是uid in (1,2,3)。那么满足uid=1或者2或者3的都查询到。
如何做到每满足一个条件只取一条?
例如uid为1,2,3分别都几条,通过sql查询,只查询uid为1的第一条,uid为2的第一条,uid为3的第一条。
------解决方案--------------------
首先你的数据当中必须有一个id,一个uid

查询uid为1,2,3分别都几条:(假定表名为'user',表中只有两个字段,分别为id和uid)

<br />select id,count(uid) from user group by uid having uid=1 or uid=2 or uid =3;<br />
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查询uid为1的第一条:

<br />select * from user where uid=1 limit 1;<br />
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------解决方案--------------------
你可以 对查询出来的结果集 在分组 取一条
------解决方案--------------------
select * from tbl_name a <br /> where (select count(*) from tbl_name where uid=a.uid and id<a.id) = 1 and uid in (1,2,3)
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------解决方案--------------------
每个条件只取一条:
 select * from tt where uid in(1,2,3) group by uid ;
------解决方案--------------------
select  a.*  from  table a where  1> (select count(1) from table b where a.id = b.id and a.id > b.id ) and a.uid in (1,2,3)
------解决方案--------------------
select top 1 * from table group by  id 
------解决方案--------------------
group by 可以实现

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