我有开始日期和结束日期的记录，如下所示：
id start_date end_date
1 2016-01-01 2016-10-31
2 2016-06-01 2016-12-31
3 2016-06-01 2016-07-31
我必须知道每月活动的记录数（或者更好的方法是：在给定期间内所有月份的第一天）。在为2016计算时，计数看起来像这样：
jan: 1
feb: 1
mar: 1
apr: 1
may: 1
jun: 3
jul: 3
aug: 2
sep: 2
oct: 2
nov: 1
dec: 1
我想到的解决方案是创建一个TEMP TABLE，其中包含给定期间的所有适用日期：
date
2016-01-01
2016-02-01
...
这使查询非常容易：
SELECT
COUNT(*),
m.date
FROM
months m
INNER JOIN table t
ON m.date BETWEEN t.start_date AND t.end_date
GROUP BY
m.date
这将产生我正在寻找的结果。然而;我确实觉得这可以更轻松地完成。我就是不知道
有什么建议么？
最佳答案
即使看起来很丑，也可以通过以下方式进行操作：
假设您要运行报告，并且只对“某年的月份”感兴趣，则可以执行以下查询：
select m,Count(id) FROM (
SELECT 1 as m UNION
SELECT 2 as m UNION
SELECT 3 as m UNION
SELECT 4 as m UNION
SELECT 5 as m UNION
SELECT 6 as m UNION
SELECT 7 as m UNION
SELECT 8 as m UNION
SELECT 9 as m UNION
SELECT 10 as m UNION
SELECT 11 as m UNION
SELECT 12 as m) AS tabseq
CROSS JOIN x WHERE
(year (start_date) = 2016 AND year (end_date) = 2016 AND m >= month(start_date) AND m <= month(end_date)) -- starts abd ends this year
or
(year (start_date) < 2016 AND year (end_date) = 2016 AND m <= month(end_date)) -- ends this year, consider months until end of contract
or
(year (start_date) < 2016 AND year (end_date) > 2016) -- spans the year, ignore month,
or
(year (start_date) = 2016 AND year (end_date) > 2016 AND m >= month(start_date)) -- starts this year, consider months until end of year
GROUP BY m;
结果：
m count(id)
1 1
2 1
3 1
4 1
5 1
6 3
7 3
8 2
9 2
10 2
11 1
12 1