Question

我希望获得10个兰特结果，image !=''，uid分组，uid select uid from user_table where type='1'来自select * from article_table where image!='' order by rand() group by uid in (select uid from user_table where type='1') limit 10。但我的查询只返回2结果。问题出在哪里？

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Answer 1

我使用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

或者您可能希望限制uid中user_table的数量，以便更快开始：

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

我在这里假设每个用户都有很多文章。虽然它看起来更可怕，但内部选择中的order by rand()覆盖了较小的数据集，这会加快速度，而外部选择中的order by只需要处理较少的行数。

请注意，按随机值排序可能会导致严重的性能损失，因为您必须遍历与where子句匹配的整个表。有alternatives。

Answer 2

以下查询将执行此操作，

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

uid的mysql组，其中uid匹配另一个查询

2 个答案: