Question

我有一个表格，如短信，其中包含from，to，message和time列（以及其他内容）。我试图询问两个号码（from和to）之间的最新记录，而不考虑方向。

以下是该表的示例：

+--------------+-----------------+--------------------+--------------+
| from         | to              | message            | time         |
+--------------+-----------------+--------------------+--------------+
| 555-1234     | 555-9876        | I'll be there.     | 06:00        |
| 555-9876     | 555-5555        | message3           | 05:30        |
| 555-9876     | 555-1234        | Bring beer         | 05:00        |
| 555-9876     | 555-1234        | My place at 8pm    | 04:00        |
| 555-9876     | 555-5555        | message2           | 03:45        |
| 555-5555     | 555-9876        | message1           | 03:30        |
| 555-9876     | 555-1234        | Are you coming?    | 03:00        |
| 555-1234     | 555-9876        | Yeah, what's up?   | 02:00        |
| 555-9876     | 555-1234        | Are you there?     | 01:00        |
+--------------+-----------------+--------------------+--------------+

我想从这个例子中得到以下记录：

+--------------+-----------------+--------------------+--------------+
| from         | to              | message            | time         |
+--------------+-----------------+--------------------+--------------+
| 555-1234     | 555-9876        | I'll be there.     | 06:00        |
| 555-9876     | 555-5555        | message3           | 05:30        |
+--------------+-----------------+--------------------+--------------+

我如何要求这些？

Answer 1

SELECT t1.*
FROM yourTable t1
INNER JOIN
(
    SELECT LEAST(`from`, `to`) AS `from`,
           GREATEST(`from`, `to`) AS `to`,
           MAX(`time`) AS `max_time`
    FROM yourTable
    GROUP BY LEAST(`from`, `to`),
             GREATEST(`from`, `to`)
) t2
    ON LEAST(t1.`from`, t1.`to`)    = t2.`from` AND
       GREATEST(t1.`from`, t1.`to`) = t2.`to`   AND
       t1.`time` = t2.`max_time`

顺便说一下，命名列from（MySQL关键字）的原因是什么？请使用其他名称。

Answer 2

你coynd使用带有max和tuple的子查询

select * from my_table 
where (from, to, time) in ( select from, to, max(time) 
                            from my_table
                            group by from, to)

Answer 3

<ul class="nav nav-tabs" id="sortable" data-bind="foreach: pcsList">

    <li>
        <a data-bind="attr: {href: '#' + id}, text: pcName"></a>
    </li>
</ul>

http://rextester.com/RDTZAK70241

MySQL：按两列分组而不考虑订单

3 个答案: