mysql使用count+group by 日期,无数据的日期补0方法

1、先用一个查询把指定日期范围的日期列表搞出来

-- t_device 为任意表,只需要数据量大于要统计的天数
SELECT
	@cdate := date_add(@cdate, INTERVAL - 1 DAY) AS statisName,
	0 AS count
FROM
	(
		SELECT
			@cdate := date_add(CURDATE(), INTERVAL + 1 DAY)
		FROM
			t_device
	) tmp
WHERE
	@cdate > date_format('2019-09-01 00:00:00', '%Y-%m-%d')

2、业务统计查询也按上述日期查询给统计日期和数量设置别名

-- t_event为要统计数据的表
SELECT
	date_format(m.CREATE_TIME, '%Y-%m-%d') AS statisName,
	count(*) AS count
FROM
	t_event AS m
WHERE
	CREATE_TIME >=  '2019-09-01 00:00:00'
GROUP BY
	date_format(m.CREATE_TIME, '%Y-%m-%d')

3、把两个查询用左连接合起，没数量的日期填0

SELECT
	t1.statisName,
	COALESCE (t2.count, 0) AS count
FROM
	(
		SELECT
			@cdate := date_add(@cdate, INTERVAL - 1 DAY) AS statisName,
			0 AS count
		FROM
			(
				SELECT
					@cdate := date_add(CURDATE(), INTERVAL + 1 DAY)
				FROM
					t_device
			) tmp
		WHERE
			@cdate > date_format('2019-09-01 00:00:00', '%Y-%m-%d')
) t1
		LEFT JOIN (
			SELECT
				date_format(m.CREATE_TIME, '%Y-%m-%d') AS statisName,
				count(*) AS count
			FROM
				t_event AS m
			WHERE
				CREATE_TIME >= '2019-09-01 00:00:00'
			GROUP BY
				date_format(m.CREATE_TIME, '%Y-%m-%d')
		) t2 ON t1.statisName = t2.statisName

缺点:统计出来的日期没有排序.