Query involving data from same query... (1 Viewer)

[JaedenRuiner]

I'm trying to do a computed column that bases its value off of a current value and subtracting a previous value.

I can be assured there is only 1 entry per Item/Person/month.

so basically if i'm looking at 1/feb/2010 wanted to subtract Amount column from the 1/jan/2010 record for the same person code and item code. Is there anyway to achieve this without using a custom function.

Currently I simply call out to a function i wrote that loads a readonly snapshot recordset and returns the computed value from the current record's data. (i pass into the Amount, ItemCode, PersonCode, and Entrydate). Is this the only way to achieve this?
Thanks
Jaeden "Sifo Dyas" al'Raec Ruiner

 

[pbaldy]

Here's a SQL method:

http://www.baldyweb.com/PrevValue.htm

 

[JaedenRuiner]

Cool. I suspected using nested queries, but wasn't sure if access was going to complain. Thanks!
J"SD"a'RR