mysql不同时间粒度下的分组统计
我们在做项目或者数据分析时，经常遇到这样的需求：统计不同时间粒度下的数据分布情况，例如，每一天中每个小时网站的访问量，某路口每半个小时通过的车辆数量等。对于此类的问题，一个sql简单的查询就能实现，故特此记录下，方便以后使用。
在MySQL中，我的表为：track
数据结构如下所示：
按天统计
SELECT DATE(TimeStart) AS date, COUNT(*) AS num
FROM track
WHERE Flag = 0 AND Duration >= 300
GROUP BY date
ORDER BY date;
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按小时统计
SELECT DATE_FORMAT(TimeStart, '%Y-%m-%d %H:00:00') AS time, COUNT(*) AS num
FROM track
WHERE Flag = 0 AND Duration >= 300
GROUP BY time
ORDER BY time;
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结果如下：
按半小时统计
SELECT time, COUNT( * ) AS num
FROM
(
SELECT Duration,
DATE_FORMAT(
concat( date( TimeStart ), ' ', HOUR ( TimeStart ), ':', floor( MINUTE ( TimeStart ) / 30 ) * 30 ),
'%Y-%m-%d %H:%i'
) AS time
FROM tarck
WHERE Flag = 0 AND Duration >= 300
) a
GROUP BY DATE_FORMAT( time, '%Y-%m-%d %H:%i' )
ORDER BY time;
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结果如下：
按N分钟统计
将上面的SQL语句稍微修改下，就可以实现按任意N分钟为时间片的分组统计，如按10分钟统计，先上代码：
SELECT time, COUNT( * ) AS num
FROM
(
SELECT Duration,
DATE_FORMAT(
concat( date( TimeStart ), ' ', HOUR ( TimeStart ), ':', floor( MINUTE ( TimeStart ) / 10 ) * 10 ),
'%Y-%m-%d %H:%i'
) AS time
FROM tarck
WHERE Flag = 0 AND Duration >= 300
) a
GROUP BY DATE_FORMAT( time, '%Y-%m-%d %H:%i' )
ORDER BY time;
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基本思路：
将datetime类型的时间转化为相应时间片的时间，例如将‘2017-03-01 01:08:19’ 转化为‘2017-03-01 01:00:00’，然后group by即可。
按分钟统计
将按小时统计的SQL语句稍微修改下，就可以实现按分钟统计
SELECT DATE_FORMAT(TimeStart, '%Y-%m-%d %H:%i:00') AS time, COUNT(*) AS num
FROM track
WHERE Flag = 0 AND Duration >= 300
GROUP BY time
ORDER BY time;
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DATE_FORMAT功能强大，可以根据format字符串格式化date值，参考下面链接
http://www.w3school.com.cn/sql/func_date_format.asp
参考博客：
- https://blog.csdn.net/kaka_buka/article/details/52614643
- https://blog.csdn.net/Beingccccc/article/details/78685490
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