need help with a formula (1 Viewer)

[dmnmak]

For my report I would like to have crystal pull up the previous months sales data. So for example if this month is October 2009, then I would want September 2009 sales.

But I've come across a problem that I need help with, let's say that the current month is January 2010, then I would want Sales data for December of 2009. I don’t know of a formula since I would be pulling data from the previous year.

So if here is my basic formula that I have. (I need help with the first line).

If Month (CurrentDate)=1 then (Need help here);
If Month (CurrentDate)=2 then {IM9_ItemSalesDetailWhse.QtySoldPeriod1};
If Month (CurrentDate)=3 then {IM9_ItemSalesDetailWhse.QtySoldPeriod2};
If Month (CurrentDate)=4 then {IM9_ItemSalesDetailWhse.QtySoldPeriod3};
If Month (CurrentDate)=5 then {IM9_ItemSalesDetailWhse.QtySoldPeriod4};
If Month (CurrentDate)=6 then {IM9_ItemSalesDetailWhse.QtySoldPeriod5};
If Month (CurrentDate)=7 then {IM9_ItemSalesDetailWhse.QtySoldPeriod6};
If Month (CurrentDate)=8 then {IM9_ItemSalesDetailWhse.QtySoldPeriod7};
If Month (CurrentDate)=9 then {IM9_ItemSalesDetailWhse.QtySoldPeriod8};
If Month (CurrentDate)=10 then {IM9_ItemSalesDetailWhse.QtySoldPeriod9};
If Month (CurrentDate)=11 then {IM9_ItemSalesDetailWhse.QtySoldPeriod10};
If Month (CurrentDate)=12 then {IM9_ItemSalesDetailWhse.QtySoldPeriod11}
else 0

Thanks to anyone that can help me, I really appreciate it.

 

[Kempes]

Not sure if help is still required but you don't need to over complicate it.
All you really need to do is open up your selection criteria, and providing you are capturing the date for each record, select this field and choose = lastfullmonth
That should do the job.