MYSQL如何计算数据存在多少小时

Question

我正在尝试计算数据库中一天中有多少小时有数据。

我使用这个查询：

SELECT
HOUR(date) AS `hour`, COUNT(date)
FROM fb_posts 
WHERE DATE(date) = CURDATE() - INTERVAL 1 DAY
GROUP BY hour

I got the query from here

示例：

hour           COUNT(date)
00             55
01             2
02             33

现在我想计算有多少小时的数据？ 上面的例子应该输出值 3，因为在 00、01 和 02 小时有数据

有些东西想像这样添加 COUNT(hour)：

SELECT
HOUR(date) AS `hour`, COUNT(date)**,COUNT(hour)**
FROM fb_posts 
WHERE DATE(date) = CURDATE() - INTERVAL 1 DAY
GROUP BY hour

Answer 1

select count(*) 
from
(
  SELECT HOUR(date) AS hour
  FROM fb_posts 
  WHERE DATE(date) = CURDATE() - INTERVAL 1 DAY
  GROUP BY hour
) tmp

Answer 2

你正在寻找count(distinct column)https://dev.mysql.com/doc/refman/5.0/en/group-by-functions.html#function_count-distinct

  SELECT count(distinct HOUR(date)) AS distinct_hour_count
  FROM fb_posts 
  WHERE DATE(date) = CURDATE() - INTERVAL 1 DAY