mysql group by uid其中与uid匹配的另一个查询

我想要获得10 rand结果，其中image !=''，uid组和uid和这些uid与select uid from user_table where type='1'相同。但我的查询只返回2结果。哪里有问题？mysql group by uid其中与uid匹配的另一个查询

select * from article_table where image!='' 
order by rand() 
group by uid 
in (select uid from user_table where type='1') 
limit 10

来源

2012-03-04 fish man

我会用join代替

select * 
    from article_table at 
    join (select uid 
      from user_table 
      where type = '1') ut 
    on at.uid = ut.uid 
where image != '' 
group by at.uid 
order by rand() 
limit 10

做，或你可能想从您user_table限制uid的数目，以使其更快地首先：

select at.* 
    from article_table at 
    join (select uid 
      from user_table 
      where type = '1' 
      order by rand() 
      limit 10) ut 
    on at.uid = ut.uid 
where image != '' 
group by at.uid 
order by rand() 
limit 10

我假设这里有很多文章给每个用户。虽然它看起来更可怕，但内部select中的order by rand()超过了一个较小的数据集，这会加快速度，外部select中的order by只能处理较少数量的行。

要小心，按照随机值排序可能会导致显着的性能下降，因为您必须遍历与where子句匹配的整个表。有alternatives。

来源

2012-03-04 12:34:33 Ben

这下面的查询将做到这一点，

SELECT * 
FROM article_table 
WHERE image!='' 
     AND uid IN (SELECT DISTINCT uid 
        FROM user_table 
        WHERE TYPE = '1' 
        LIMIT 10) 
GROUP BY uid 
ORDER BY Rand() 
LIMIT 10

来源

2012-03-04 12:34:55

mysql group by uid其中与uid匹配的另一个查询

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