Find total number in a specific period of time SQL - tsql

Question

I am trying to find the total number of members in a given period. Say I have the following data:
member_id start_date end_date
1 9/1/2013 12/31/2013
2 10/1/2013 11/12/2013
3 12/1/2013 12/31/2013
4 5/1/2012 8/5/2013
5 9/1/2013 12/31/2013
6 7/1/2013 12/31/2013
7 6/6/2012 12/5/2013
8 10/1/2013 12/31/2013
9 7/8/2013 12/31/2013
10 1/1/2012 11/5/2013
In SQL I need to create a report that will list out the number of members in each month of the year. In this case something like the following:
Date Members Per Month
Jan-12 1
Feb-12 1
Mar-12 1
Apr-12 1
May-12 2
Jun-12 3
Jul-12 3
Aug-12 3
Sep-12 3
Oct-12 3
Nov-12 3
Dec-12 3
Jan-13 3
Feb-13 3
Mar-13 3
Apr-13 3
May-13 3
Jun-13 3
Jul-13 5
Aug-13 4
Sep-13 6
Oct-13 8
Nov-13 6
Dec-13 6
So there is only 1 member from Jan-12 (member id 10) until May-12 when member id 4 joins making the count 2 and so on.
The date range can be all over so I can't specify the specific dates but it is by month, meaning that even if someone ends 12-1 it is considered active for the month for Dec.

Answer 1

I was able to create the following stored procedure that was able to accomplish what I needed:
USE [ValueBasedSandbox]
GO
/****** Object: StoredProcedure [dbo].[sp_member_count_per_month] Script Date: 01/08/2015 12:02:37 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Create date: 2015-08-01
-- Description: Find the counts per a given date passed in
-- =============================================
CREATE PROCEDURE [dbo].[sp_member_count_per_month]
-- Add the parameters for the stored procedure here
#YEAR int
, #ENDYEAR int
AS
DECLARE #FIRSTDAYMONTH DATETIME
DECLARE #LASTDAYMONTH DATETIME
DECLARE #MONTH INT = 1;
--Drop the temporary holding table if exists
IF OBJECT_ID('tempdb.dbo.##TEMPCOUNTERTABLE', 'U') IS NOT NULL
DROP TABLE dbo.##TEMPCOUNTERTABLE
CREATE TABLE dbo.##TEMPCOUNTERTABLE (
counter INT
, start_date DATETIME2
, end_date DATETIME2
)
--Perform this loop for each year desired
WHILE #YEAR <= #ENDYEAR
BEGIN
--Perform for each month of the year
WHILE (#MONTH <= 12)
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
SET #FIRSTDAYMONTH = DATEADD(MONTH, #MONTH - 1, DATEADD(YEAR, #YEAR-1900, 0))
SET #LASTDAYMONTH = DATEADD(MONTH, #MONTH, DATEADD(YEAR, #YEAR-1900, 0)-1)
INSERT INTO dbo.##TEMPCOUNTERTABLE(counter, start_date, end_date)
SELECT COUNT(*) AS counter
, #FIRSTDAYMONTH AS start_date
, #LASTDAYMONTH AS end_date
FROM dbo.member_table
WHERE start_date <= #LASTDAYMONTH
AND end_date >= #FIRSTDAYMONTH
--Increment through all the months of the year
SET #MONTH = #MONTH + 1
END -- End Monthly Loop
--Reset Month counter
SET #MONTH = 1
--Increment the desired years
SET #YEAR = #YEAR + 1
END -- End Yearly Loop
--Display the results
SELECT *
FROM dbo.##TEMPCOUNTERTABLE
-- Drop the temp table
IF OBJECT_ID('tempdb.dbo.##TEMPCOUNTERTABLE', 'U') IS NOT NULL
DROP TABLE dbo.##TEMPCOUNTERTABLE
GO

Answer 2

This should do the trick
with datesCte(monthStart,monthEnd) as
(
select cast('20120101' as date) as monthStart, cast('20120131' as date) as monthEnd
union all
select DATEADD(MONTH, 1, d.monthStart), dateadd(day, -1, dateadd(month, 1, d.monthStart))
from datesCte as d
where d.monthStart < '20140101'
)
select *
from datesCte as d
cross apply
(
select count(*) as cnt
from dbo.MemberDates as m
where m.startDate <= d.monthEnd and m.endDate > d.monthStart
) as x
order by d.monthStart