I have two tables. one is stock
and the other one is shipping information
Example Table Stock
PARTNO QTYONHAND
A 50
B 25
C 5
D 10
E 20
EXAMPLE OF TABLE SHIP
CUSTOMER PTNO SHIPQTY DIFFERENCE
ABC A 45 5
BDF A 10 -5
CDF A 50 -55
AER B 1 24
I Don't know how to get the difference...