SQL：GROUP BY之后的SUM

SQL：GROUP BY之后的SUM

[sql fiddle demo](http://www.sqlfiddle.com/#!3/811a6/3/0)

此SQL Fiddle解决了您的疑虑。您需要生成一个Calendar表，以便您可以将日期添加到其中。然后，您可以为每个客户计算不同的MonthYears。

create table test(  CustomerId int,  StartDate date,  EndDate date  )insert into testvalues   (10, '9/1/2013', '9/30/2013'),  (10, '9/1/2013', '9/30/2013'),  (11, '9/1/2013', '11/30/2013'),  (11, '9/1/2013', '11/30/2013'),  (11, '9/1/2013', '11/30/2013'),  (10, '10/1/2013', '12/31/2013'),  (10, '10/1/2013', '12/31/2013'),  (11, '12/1/2013', '4/30/2014')create table calendar(  MY varchar(10),  StartDate date,  EndDate date  )insert into calendarvalues   ('9/2013', '9/1/2013', '9/30/2013'),  ('10/2013', '10/1/2013', '10/31/2013'),  ('11/2013', '11/1/2013', '11/30/2013'),  ('12/2013', '12/1/2013', '12/31/2013'),  ('1/2014', '1/1/2014', '1/31/2014'),  ('2/2014', '2/1/2014', '2/28/2014'),  ('3/2014', '3/1/2014', '3/31/2014'),  ('4/2014', '4/1/2014', '4/30/2014')select  t.CustomerId,   count(distinct c.MY)from  test t  inner join calendar c    on t.StartDate <= c.EndDate      and t.EndDate >= c.StartDategroup by  t.CustomerId