mysql查询,如何使用GROUP_CONCAT获得前5个下载

Question

MySql表中的以下数据.

brand_id|image_id|downloads
--------|--------|---------
8       |9       |8    
35      |2829    |4    
28      |2960    |3    
28      |2961    |3    
28      |3041    |3    
35      |2831    |3    
28      |2965    |3    
35      |2832    |3    
28      |2959    |2    
28      |2976    |2    
35      |2894    |2  

如何GROUP_CONCAT在每个品牌中找到具有功能的前5个图像我想跟随返回

brand_id|image_ids                
--------|--------------------------
8       |9                       
35      |2829,2831,2832,2894     
28      |2960,2961,3041,2965,2959

以下查询提供预期结果

SELECT brand_id, SUBSTRING_INDEX(GROUP_CONCAT(image_id SEPARATOR ','),',',5) AS image_ids
FROM Table1
GROUP BY brand_id

我有一个大量的数据约2MILION记录表和brand_id,image_id都重复每个用户下载所以当我运行查询我得到以下错误

MySql Error: %d line(s) were cut by GROUP_CONCAT()

我认为GROUP_CONCAT范围超出了,你能不能提供解决方案,所以每个品牌只能获得前5个下载,所以不需要SUBSTRING_INDEX功能.

谢谢

Answer 1

试试这个:

SELECT brand_id, GROUP_CONCAT(image_id) image_ids
FROM (SELECT brand_id, image_id, 
             IF(@lastBrandId = @lastBrandId:=brand_id, @Idx:=@Idx+1, @Idx:=0) rowNumber 
      FROM Table1, (SELECT @lastBrandId:=0, @Idx:=0) A
      ORDER BY brand_id, downloads DESC
     ) AS A
WHERE rowNumber < 5
GROUP BY brand_id