mysql统计前24小时数据没有补0

SELECT
   t1. HOUR HOUR,
   COUNT(t2. HOUR) count
FROM
   (
      SELECT
         DATE_FORMAT(
            @cdate := DATE_ADD(@cdate, INTERVAL - 1 HOUR),
            '%y-%m-%d %H'
         ) HOUR
      FROM
         (
            SELECT
               @cdate := DATE_ADD(
                  DATE_FORMAT(NOW(), '%y-%m-%d %H'),
                  INTERVAL + 1 HOUR
               )
            FROM
               city
         ) t0
      LIMIT 24
   ) t1
LEFT JOIN (
   SELECT
      DATE_FORMAT(visit_time, '%y-%m-%d %H') HOUR
   FROM
      visit_log
   WHERE
      visit_time >= (NOW() - INTERVAL 24 HOUR)
) t2 ON t1. HOUR = t2. HOUR
GROUP BY
   t1. HOUR
ORDER BY
   t1. HOUR DESC

查询当前时间前24小时日期天数

SELECT
         DATE_FORMAT(
            @cdate := DATE_ADD(@cdate, INTERVAL - 1 HOUR),
            '%y-%m-%d %H'
         ) HOUR
      FROM
         (
            SELECT
               @cdate := DATE_ADD(
                  DATE_FORMAT(NOW(), '%y-%m-%d %H'),
                  INTERVAL + 1 HOUR
               )
            FROM
               city  #记录大于等于24条的任意一张表
         ) t0
      LIMIT 24

查询前24小时有的数据

SELECT
      DATE_FORMAT(visit_time, '%y-%m-%d %H') HOUR
   FROM
      visit_log  #真正要查的记录表
   WHERE
      visit_time >= (NOW() - INTERVAL 24 HOUR)

最后结果

参考https://www.cnblogs.com/dennyzhangdd/p/8073181.html