php - MySQL 按类别分组，每个类别限制 N 个

Question

表格

id       title        category

<小时/>

1        hello1          1
2        hello2          2
3        hello3          1

查询

select  *
from    videos
where   category in
        (
        select  category
        from    videos
        group by 
               category
        having 
               count(*) < 3
ORDER BY RAND()
        )

我的目标是以随机顺序从每个类别中获得 2 个标题 我也想以这种方式获取记录

category1
title1
title2

<小时/>

category2
title1
title2

Answer 1

以下查询给出每个类别中不超过两个随机行:

SELECT title, category
FROM (
  SELECT v.*,
     if( category = @last_cat,
         if( @last_cat:=category, @x:=@x+1,@x:=@x+1),
         if( @last_cat:=category, @x:=0,@x:=0)
     ) x
  FROM (SELECT @last_cat:=-9876, @x:=-91234) x,
       (SELECT * FROM videos ORDER BY category, rand()) v
) x
WHERE x < 2

演示:http://sqlfiddle.com/#!2/59cf9/8