我有一个名为category的表,该表具有3列：id,name,parent_id.

ID         name         group_id
==         ==           ==
1          haim         1
2          gil          2
3          alon         1
4          idan         1
5          shai         3
6          adi          2
7          itay         3
8          aviram       1
9          lioz         3
10         amit         2
11         ben          2
12         eran         1

我需要在一个查询中选择每个group_id 2行,所以结果将是：

ID         name         group_id
==         ==           ==
1          haim         1
3          alon         1
2          gil          2
6          adi          2
5          shai         3
7          itay         3

非常重要的一点是,它也将按group_id进行排序.

谢谢！

解决方法:

我考虑了每个group_id在表中找到的第一个和第二个ID.

SELECT ID, NAME, GROUP_ID
FROM MYTABLE WHERE ID IN (
    SELECT MIN(ID)
    FROM MYTABLE
    GROUP BY GROUP_ID)

UNION ALL

SELECT ID, NAME, GROUP_ID
FROM MYTABLE WHERE ID IN (
    SELECT MIN(ID)
    FROM MYTABLE
    WHERE ID NOT IN (
      SELECT MIN(ID)
      FROM MYTABLE
      GROUP BY GROUP_ID
      )
    GROUP BY GROUP_ID)
ORDER BY GROUP_ID