表结构和数据如下：
id userid isquoted
1 69355164 0
4 69355164 1
5 69355164 1
6 11D8952A 1
查询要求：userid唯一，isquoted=0优先
结果如下：
1 69355164 0
6 11D8952A 1
费了半天劲，不知道还有没有更好的办法：
-----------查询 ：userid唯一，isquoted=0优先------
select id,userid,0 as isquoted from quote_s_info
where isquoted = 0
group by userid ,id
union
select id,userid,1 as isquoted from quote_s_info
where isquoted = 1 and userid not in
(
select userid from quote_s_info where isquoted = 0 group by userid
)
group by userid,id
----------------
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