distinct count for sevral months

[curious]

I have a table with for every customer a record with (amongst others) all months of a year and the month of subscription

example

customnumber month month of subscription
1 201201 201201
1 201202 201201
1 201203 201201
1 201204 201201
1 201205 201201
2 201203 201203
2 201204 201203
2 201205 201203
etc.

I use next expression :

If ([month_subcribe]= [month of subscription] then (count(distinct [customnumber]) else (0)

When I create a report with the colums month and number of new subscriptions
I only get a result for the first month, so the result for 201201 = 1 but the result for 201303 = 0

What expression do I have to use to get correct results ?



Thanks in advance

[hittony]

I suppose that a customer can't subscribe twice in the same month, so the number of new subscriptions could be defined like this :

Total( If ([month_subcribe]= [month of subscription] then (1) else (0) )

[curious]

@hittony : Indeed a customer can not subsbribe twice in the same month, but he can take two subscriptions in the same month. I want the customer counted once.

In the mean time I found a solution. I created an extra field indicating  whether a customer subscribes (=1)  and then counted distinct customnumber where new field =1