有没有办法从每组行中获取2行？

Question

  

可能重复：
  How do I select a fixed number of rows for each group?

例如......如果我有这个表（按颜色排序）：

--------------
| id | color |
--------------
| 95 | red   |
| 7  | red   |
| 44 | red   |
| 46 | red   |
| 49 | red   |
| 24 | green |
| 37 | green |
| 91 | green |
| 88 | green |
| 44 | blue  |
| 10 | blue  |
| 11 | blue  |
--------------

我有办法从每种颜色中获取2行吗？例如：

--------------
| id | color |
--------------
| 7  | red   |
| 44 | red   |
| 24 | green |
| 37 | green |
| 10 | blue  |
| 11 | blue  |
--------------

Answer 1

你可以拥有这样的东西，

SELECT id, color
FROM   TableName a
WHERE 
(
   SELECT COUNT(*) 
   FROM   TableName AS f
   WHERE  f.color = a.color AND f.id <= a.id
) <= 2;

• SQLFiddle Demo