Question

这是一些测试数据。

+----+------+-------+---------+---------+
| id | type | param | enabled | account | 
+----+------+-------+---------+---------+
|  1 | test |     a |       1 |    null |
|  2 | asdf |     b |       1 |    null |
|  3 | test |     c |       1 |      34 |
|  4 | test |     d |       0 |      34 |
|  5 | asdf |     e |       1 |    null |
+----+------+-------+---------+---------+

我想选择最新的行，其中＆＃34;键入＆＃34;和＆＃34;帐户＆＃34;是独一无二的。

例如，对于该测试表，我想要结果：

+----+------+-------+---------+---------+
| id | type | param | enabled | account | 
+----+------+-------+---------+---------+
|  1 | test |     a |       1 |    null |
|  4 | test |     d |       0 |      34 |
|  5 | asdf |     e |       1 |    null |
+----+------+-------+---------+---------+

我尝试过GROUP BY的变体：

SELECT * FROM test GROUP BY type, account

由于某种原因，这给了我：

+----+------+-------+---------+---------+
| id | type | param | enabled | account | 
+----+------+-------+---------+---------+
|  1 | test |     a |       1 |    null |
|  4 | test |     d |       1 |      34 | <- note that enabled is taking on an incorrect value.
|  5 | asdf |     e |       1 |    null |
+----+------+-------+---------+---------+

这样做的正确方法是什么？

Answer 1

假设＆＃34;最新的行＆＃34;表示具有最大id的那个，那么有几种方法。使用in的方法是：

SELECT t.*
FROM test t
WHERE t.id IN (SELECT MAX(id) FROM test t2 GROUP BY type, account)

Answer 2

如果您的查询为您提供了正确的ID，您应该尝试将其放入子查询中：

SELECT * FROM test WHERE id IN (SELECT id FROM test GROUP BY type, account)

选择一些不同的列

2 个答案: