Mysql 查询一天中，每个小时数据的数量

其中 created_at 是时间戳，如果是时间格式那么无需 FROM_UNIXTIME 转换。

SELECT
    HOUR (FROM_UNIXTIME(created_at)) AS Hour,
    count(*) AS Count
FROM
    yun_user
WHERE
    FROM_UNIXTIME(created_at, '%Y-%m-%d') = '2018-01-03'
GROUP BY
    HOUR (FROM_UNIXTIME(created_at))
ORDER BY
    HOUR (FROM_UNIXTIME(created_at));

SELECT
    FROM_UNIXTIME(created_at,'%H') AS Hour,
    count(*) AS Count
FROM
    yun_user
WHERE
    FROM_UNIXTIME(created_at, '%Y-%m-%d') = '2018-01-03'
GROUP BY
    FROM_UNIXTIME(created_at,'%H')
ORDER BY
    FROM_UNIXTIME(created_at,'%H');