Cumulative SQL to work out no of payers - sql-server-2008

Question

Currently trying to create a query that shows how many accounts have paid month on month but on a cumulative basis (penetration). So as an example I have a table with Month paid and account number, which shows what month that account paid.
Month | AccountNo
Jan-14 | 123456
Feb-14 | 321654
So using the above the result set would show
Month | Payers
Jan-14 | 1
Feb-14 | 2
being because one account paid in Jan, then one in Feb meaning that there have been by the end of Feb 2 payments overall, but only one in Jan. Tried a few inner joins back onto the table itself with a t1.Month >= t2.Month as i would for a normal cumulative query but the result is always out.
Any questions please ask, unsure if the above will be clear to anyone but me.

Answer 1

If you have date in the table then you can try the following query.
SELECT [Month]
,(SELECT COUNT(AccountNo)
FROM theTable i
-- This is to make sure to add until the last day of the current month.
WHERE i.[Date] <= DATEADD(s,-1,DATEADD(mm, DATEDIFF(m,0,o.[Date])+1,0)) AS CumulativeCount
FROM theTable o

Answer 2

Ok, several things. You need to have an actual date field, as you can't order by the month column you have.
You need to consider there may be gaps in the months - i.e. some months where there is no payment (not sure if that is true or not)
I'd recommend a recursive common table expression to do the actual aggregation
Heres how it works out:
-- setup
DECLARE #t TABLE ([Month] NCHAR(6), AccountNo INT)
INSERT #t ( [Month], AccountNo )
VALUES ( 'Jan-14',123456),('Feb-14',456789),('Apr-14',567890)
-- assume no payments in march
; WITH
t2 AS -- get a date column we can sort on
(
SELECT [Month],
CONVERT(DATETIME, '01 ' + REPLACE([Month], '-',' '), 6) AS MonthStart,
AccountNo
FROM #t
),
t3 AS -- group by to get the number of payments in each month
(
SELECT [Month], MonthStart, COUNT(1) AS PaymentCount FROM t2
GROUP BY t2.[Month], t2.MonthStart
),
t4 AS -- get a row number column to order by (accounting for gaps)
(
SELECT [Month], MonthStart, PaymentCount,
ROW_NUMBER() OVER (ORDER BY MonthStart) AS rn FROM t3
),
t5 AS -- recursive common table expression to aggregate subsequent rows
(
SELECT [Month], MonthStart, PaymentCount AS CumulativePaymentCount, rn
FROM t4 WHERE rn = 1
UNION ALL
SELECT t4.[Month], t4.MonthStart,
t4.PaymentCount + t5.CumulativePaymentCount AS CumulativePaymentCount, t4.rn
FROM t5 JOIN t4 ON t5.rn + 1 = t4.rn
)
SELECT [Month], CumulativePaymentCount FROM t5 -- select desired results
and the results...
Month CumulativePaymentCount
Jan-14 1
Feb-14 2
Apr-14 3

Answer 3

If your month column is date type then its easy to work on else you need some additional conversion for it. Here the query goes...
create table example (
MONTHS datetime,
AccountNo INT
)
GO
insert into example values ('01/Jan/2009',300345)
insert into example values ('01/Feb/2009',300346)
insert into example values ('01/Feb/2009',300347)
insert into example values ('01/Mar/2009',300348)
insert into example values ('01/Feb/2009',300349)
insert into example values ('01/Mar/2009',300350)
SELECT distinct datepart (m,months),
(SELECT count(accountno)
FROM example b
WHERE datepart (m,b.MONTHS) <= datepart (m,a.MONTHS)) AS Total FROM example a