请问我从类似下图所示的数据集中查询每个类别的前N个问题。我已经看到了各种各样的线程,但是我在查询我的具体问题时遇到了问题。
+----+---------------------------------+-------+
| ID | Prod |Cat Id |
+----+---------------------------------+-------+
| 1 | kntrn | 1 |
| 2 | kntrn e | 1 |
| 3 | e spl | 1 |
| 4 | spl php | 1 |
| 5 | php cicarredgtal | 1 |
| 6 | cicarredgtal servecounterstrike | 1 |
| 7 | servecounterstrike com | 1 |
| 8 | zlv | 2 |
| 9 | zlv enter | 2 |
| 10 | spl php | 2 |
+----+---------------------------------+-------+
我想根据这条规则进行分组(1)为每个catid选择Top 3 Prod。
请注意,这个意义上的顶部是所有类别中最高的刺激数。
因此,对于上面的示例,spl php是catID 1的最高值,因为它在所有类别中出现两次。
答案 0 :(得分:1)
这可能不是很漂亮,但我认为它会起作用:
SELECT cat_id, prod, pos FROM (
SELECT cat_id, pos, prod, if(@last_id = cat_id, @cnt := @cnt + 1, (@cnt := 0 || @last_id := cat_id)) cnt
FROM (
SELECT p.cat_id, pseq.cnt pos, pseq.prod
FROM (
SELECT prod, count(*) cnt FROM prods GROUP BY prod ORDER BY cnt DESC
) pseq
INNER JOIN prods p ON p.prod = pseq.prod
ORDER BY cat_id, pseq.cnt DESC
) po
) plist
WHERE cnt <= 3;
Based on the above data, this will return:
+--------+-----------+-----+
| cat_id | prod | pos |
+--------+-----------+-----+
| 1 | spl php | 2 |
| 1 | kntrn | 1 |
| 1 | kntrn e | 1 |
| 2 | spl php | 2 |
| 2 | zlv | 1 |
| 2 | zlv enter | 1 |
+--------+-----------+-----+