mysql - 基于日期时间查询最近的最佳方法(MySQL)

Question

如果我有一个表来存储一个人的名字、他们跑一英里所花费的时间以及他们跑一英里的时间，那么获取一个人最近的单圈时间的最佳方法是什么。

LAPS
____________________________________________
|  name   | lap_time |        date         |
--------------------------------------------
| George  |   20.3   | 2013-01-17 09:17:14 |
| Alex    |   32.2   | 2013-02-17 14:24:32 |         
| Mike    |   16.6   | 2013-01-17 07:57:54 |
| Alex    |   28.5   | 2013-01-17 19:50:21 |
| Mike    |   15.1   | 2013-02-17 12:37:12 |
| Mike    |   14.8   | 2013-03-17 06:58:34 |
''''''''''''''''''''''''''''''''''''''''''''

我一直在这样做，到目前为止它对我有用，但我很想知道是否有更好的方法。

SELECT l.lap_time
FROM laps l
INNER JOIN(
    SELECT *, MAX(date) as most_recent
    FROM laps
    WHERE name = 'Alex'
)AS temp ON (
    l.date = temp.most_recent
    AND l.name = temp.name
)

我使用此类查询的实际表很大，因此我正在寻找最省时的方法。

Answer 1

这适用于单个名称:

SELECT name, lap_time, date
FROM laps
WHERE name = 'Alex'
ORDER BY date DESC
LIMIT 1

结果

| NAME | LAP_TIME |                            DATE |-----------------------------------------------------| Alex |     32.2 | February, 17 2013 14:24:32+0000 |

See the demo

This should work for all names:

SELECT a.name, b.lap_time, a.date
FROM
  (SELECT name, MAX(date) AS date FROM laps GROUP BY name) a
LEFT JOIN laps b 
  ON b.date = a.date AND b.name = a.name

结果

|   NAME | LAP_TIME |                            DATE |-------------------------------------------------------|   Alex |     32.2 | February, 17 2013 14:24:32+0000 || George |     20.3 |  January, 17 2013 09:17:14+0000 ||   Mike |     14.8 |    March, 17 2013 06:58:34+0000 |

See the demo