MySQL如何按每3小时统计一天的数据？

SELECT NAME, IFNULL(count + count1, 0) AS `count`
FROM (
	SELECT t1.NAME, t.count, t1.count1
	FROM (
		SELECT CASE
				WHEN HOUR(DISCOVERTIME) BETWEEN 0 AND 3 THEN '00'
				WHEN HOUR(DISCOVERTIME) BETWEEN 3 AND 6 THEN '03'
				WHEN HOUR(DISCOVERTIME) BETWEEN 6 AND 9 THEN '06'
				WHEN HOUR(DISCOVERTIME) BETWEEN 9 AND 12 THEN '09'
				WHEN HOUR(DISCOVERTIME) BETWEEN 12 AND 15 THEN '12'
				WHEN HOUR(DISCOVERTIME) BETWEEN 15 AND 18 THEN '15'
				WHEN HOUR(DISCOVERTIME) BETWEEN 18 AND 21 THEN '18'
				WHEN HOUR(DISCOVERTIME) BETWEEN 21 AND 23 THEN '21'
			END AS `name`, IFNULL(COUNT(1), 0) AS `count`
		FROM 表名
		WHERE 1 = 1
			-- 这里可以添加其他条件 比如 and flag=1 and type = 2 and isdelete = 0
			-- AND to_Days(DISCOVERTIME) = to_days(now())  这里不建议这么写，有to_days()这种运算的逻辑可以放到程序中去处理，没必要在数据库中去做运算，我们在开发过程中尽量避免这一点，可以参考下面这种写法，这个时间的处理可以参考我的另外一篇博客 http://www.fujiatian.com/post/24365.html
			and	DISCOVERTIME >= '2019-11-11 00:00:00' AND DISCOVERTIME < '2019-11-12 00:00:00'
		GROUP BY CASE
				WHEN HOUR(DISCOVERTIME) BETWEEN 0 AND 3 THEN 1
				WHEN HOUR(DISCOVERTIME) BETWEEN 3 AND 6 THEN 2
				WHEN HOUR(DISCOVERTIME) BETWEEN 6 AND 9 THEN 3
				WHEN HOUR(DISCOVERTIME) BETWEEN 9 AND 12 THEN 4
				WHEN HOUR(DISCOVERTIME) BETWEEN 12 AND 15 THEN 5
				WHEN HOUR(DISCOVERTIME) BETWEEN 15 AND 18 THEN 6
				WHEN HOUR(DISCOVERTIME) BETWEEN 18 AND 21 THEN 7
				WHEN HOUR(DISCOVERTIME) BETWEEN 21 AND 23 THEN 8
			END
	) t
		RIGHT JOIN (
			SELECT '00' AS NAME, 0 AS count1
			UNION
			SELECT '03' AS NAME, 0 AS count1
			UNION
			SELECT '06' AS NAME, 0 AS count1
			UNION
			SELECT '09' AS NAME, 0 AS count1
			UNION
			SELECT '12' AS NAME, 0 AS count1
			UNION
			SELECT '15' AS NAME, 0 AS count1
			UNION
			SELECT '18' AS NAME, 0 AS count1
			UNION
			SELECT '21' AS NAME, 0 AS count1
		) t1
		ON t.NAME = t1.NAME
) t