mysql - 按日期对 MYSQL 结果行进行分组

Question

我想按时间戳的小时对从 MYSQL 数据库获取的结果进行分组。时间戳以 2012-12-14 03:19:09 格式存储在表中。我使用查询

SELECT
    HOUR(`timestamp`) AS `hour`,
    AVG(`somevalue`) AS `average`
FROM ...
GROUP BY
    HOUR(`timestamp`),
    DAY(`timestamp`),
    MONTH(`timestamp`),
    WEEK(`timestamp`),
    YEAR(`timestamp`)
ORDER BY ...
LIMIT 0, 24;

这有效，并返回正确的行和值...

+------+-------+
| hour | value |
+------+-------+
| 13   | 21.16 | 
| 12   | 21.11 |
| 11   | 20.88 |
| 10   | 20.93 |
|  9   | 20.87 |
|  8   | 20.89 |
| ...  | ...   |
+------+-------+ 

...但是速度非常慢(表包含约 90k 行)。我是given the advice不是按每个日期实体分组，而是按 UNIX_TIMESTAMP(`timestamp`)/3600 分组。不幸的是，这并没有达到预期的结果，结果看起来像这样

+------+-------+
| hour | value |
+------+-------+
| 13   | 21.20 |
| 13   | 21.20 |
| 13   | 21.20 |
| 13   | 21.20 |
| 13   | 21.20 |
| ...  | ...   |
+------+-------+ 

是否有任何方法可以仅通过一个组子句对它们进行分组(这将使其更快)，但返回正确的结果？

Answer 1

不要使用按日期和时间分组

SELECT
    HOUR(`timestamp`) AS `hour`,
    AVG(`somevalue`) AS `average`
FROM ...
GROUP BY
    DATE(`timestamp`),
    HOUR(`timestamp`),
ORDER BY ...
LIMIT 0, 24;