If statement in load pulling from different table

[#1]

I have an if expression that I am using in the load script. My conditions are all from the same table but the sum field is from a different table.

if(Ship_Date__c <>''  and Booked_on_AS400__c  <>'' and Rev_Rec__c > Today(),ProductsOTR_Price,0) as RecognizedRevenue,

Is there a way to have this statement load from different tables.

Thanx