mysql选择每种类型的3个随机行

Question

我创建了以下查询:

 SELECT random.aid, random.rand_pid, r3.filepath, r3.filename, r3.pid
 FROM 
 (SELECT r.aid,
    (SELECT r2.pid
     FROM cpg_pictures r2
     WHERE r2.aid = r.aid
     ORDER BY RAND() LIMIT 1) AS 'rand_pid'
 FROM cpg_pictures r
 GROUP BY r.aid
 ORDER BY r.aid DESC
 LIMIT 10
 ) random
 LEFT JOIN cpg_pictures AS r3 ON r3.pid = rand_pid

cpg_pictures 是一个有图片的表而 aid 是相册 id

此查询将从每个相册 ID 中随机获取 1 张图片，

我希望能够修改查询以便为每个相册 ID 获取 3 张随机图片，因此，我们将不胜感激。

我还想将这个最终结果与 cpg_albums 表连接起来，其中 cpg_pictures.aid = cpg_albums.aid

Answer 1

你试过吗？

 SELECT random.aid, random.rand_pid, r3.filepath, r3.filename, r3.pid
 FROM 
 (SELECT r.aid,
    (SELECT r2.pid
     FROM cpg_pictures r2
     WHERE r2.aid = r.aid
     ORDER BY RAND() LIMIT 1) AS 'rand_pid'
 FROM cpg_pictures r
 GROUP BY r.aid
 ORDER BY r.aid DESC
 LIMIT 10
 ) random
 LEFT JOIN cpg_pictures AS r3 ON r3.pid = rand_pid

您还可以模拟此 http://beyondrelational.com/modules/2/blogs/70/posts/10845/return-top-n-rows.aspx 的 1 和 2|