Calculate numbers between 2 dates
 

Hi

I was trying to figure out the following.

If i need to calculate sales between 2 dates which are given

C1 C2 C3 C4 C5 C6
C7 C8 C9
ID FrstVis VAr1 19991230 20010228 20030531 Flag
Cumlsales #Mnth

1 19980430 20040131 431 991 756 1
? ?
2 19970630 20021130 811 555 245 0
? ?
3 19990931 20031231 823 475 386 1
? ?

I need to calculate if Flag=1, than what would be cuml sales between the
dates of Firstvis and Var1 if columns 4,5,6 gives the sales during the said
period . also for C9 , how many months did the sales happen.
eg. for ID 1 , what would be the sales between the 2 dates given in c2 and
C3, given that for ID 1, he did sales as per c4,c5,c6.

THanks

Rajiv