MySQL查询两个表和最大时间戳

Question

我有两个看起来像这样的表:

TABLE_conversations:

+-----------------+----------+----------------+------------+---------------------+--------+
| CONVERSATION_ID | QUEUE_ID | CONTACT_NUMBER | CONTACT_ID | DATE_CREATED        | STATUS |
+-----------------+----------+----------------+------------+---------------------+--------+
|               1 |        1 | 15551112222    |    9000001 | 2014-09-12 00:28:24 | ACTIVE |
|               2 |        1 | 15553334444    |    9000002 | 2014-09-12 00:32:08 | ACTIVE |
+-----------------+----------+----------------+------------+---------------------+--------+

表消息:

+------------+-----------------+-------------+-------------+-----------+---------+---------------------+--------+-----------------------------------------------------------------------------------------------------------------+--------+
| MESSAGE_ID | CONVERSATION_ID | FROM_NUMBER | TO_NUMBER   | DIRECTION | SENDER  | TIMESTAMP          | VIEWED | MESSAGE                                                                                                         | STATUS |
+------------+-----------------+-------------+-------------+-----------+---------+---------------------+--------+-----------------------------------------------------------------------------------------------------------------+--------+
|          1 |               1 | 15551112222 | 17021112222 | IN        | 9000001 | 2014-09-12 00:30:11 |      1 | Hello!  Is this working?                                                                     | ACTIVE |
|          2 |               1 | 17021112222 | 15551112222 | OUT       | 8000001 | 2014-09-12 00:31:05 |      1 | Good evening!  Of course!  | ACTIVE |
|          3 |               1 | 15551112222 | 17021112222 | IN        | 9000001 | 2014-09-12 00:31:27 |      1 | Perfect.  Thank you!                                                                                            | ACTIVE |
|          4 |               1 | 17021112222 | 15553334444 | OUT       | 8000002 | 2014-09-12 00:32:52 |      1 | Ticket 11251 is ready for pickup.                                                                         | ACTIVE |
+------------+-----------------+-------------+-------------+-----------+---------+---------------------+--------+-----------------------------------------------------------------------------------------------------------------+--------+

我正在尝试运行查询来选择 CONVERSATION_ID、CONTACT_NUMBER、CONTACT_ID 和最近的 TIMESTAMP 并按电话号码分组:

SELECT TABLE_conversations.CONVERSATION_ID, TABLE_conversations.CONTACT_NUMBER,
       TABLE_conversations.CONTACT_ID, MAX(TABLE_messages.TIMESTAMP) 
FROM TABLE_conversations, TABLE_messages 
WHERE TABLE_conversations.STATUS='ACTIVE' 
AND TABLE_messages.STATUS='ACTIVE' 
GROUP BY CONTACT_NUMBER 
ORDER BY TABLE_messages.TIMESTAMP;

我得到的输出如下:

+-----------------+----------------+------------+-------------------------------+
| CONVERSATION_ID | CONTACT_NUMBER | CONTACT_ID | MAX(TABLE_messages.TIMESTAMP) |
+-----------------+----------------+------------+-------------------------------+
|               1 | 15551112222    |    9000001 | 2014-09-12 00:32:52           |
|               2 | 15553334444    |    9000002 | 2014-09-12 00:32:52           |
+-----------------+----------------+------------+-------------------------------+

我得到的两者的时间戳相同。我想要的结果是 2014-09-12 00:31:27 为 15551112222 和 2014-09-12 00:32:52 为 15553334444。

非常感谢任何帮助!

Answer 1

您缺少表之间的连接条件，因此您将获得完整的叉积。因此，每个对话都与每条消息相结合，而不仅仅是该对话中的消息。

SELECT TABLE_conversations.CONVERSATION_ID, TABLE_conversations.CONTACT_NUMBER,
       TABLE_conversations.CONTACT_ID, MAX(TABLE_messages.TIMESTAMP) 
FROM TABLE_conversations
JOIN TABLE_messages ON TABLE_conversations.conversation_id = TABLE_messages.conversation_id
WHERE TABLE_conversations.STATUS='ACTIVE' 
AND TABLE_messages.STATUS='ACTIVE' 
GROUP BY CONTACT_NUMBER 
ORDER BY TABLE_messages.TIMESTAMP;