More info: Sorry here is more info:

Table 1:

1 field (item_code) c(15) [total 15 records]

record: Memory

Table 2:

inv_no c(7), inv_desc c(20), inv_qty n(10)

records look like this:

'CREDIT' , M123456, Mr. Stone, 0

Table 3 (Current Table):

inv_no c(7), inv_desc c(20), inv_qty n(10)

records look like this:
'M123456', Casing, 1
'M123456', Motherboard, 1
'M123456', Memory, 2

Table 4 (Archive Table):

inv_no c(7), inv_desc c(20), inv_qty n(10)

records look like this:
'M123456', Casing, 1
'M123456', Motherboard, 1
'M123456', Memory, 2

what I am trying to utilize if the system does not have the information in the current table, thus look in the archive table. using sql to make process faster. essentially trying to find the original invoice that matches the credit and a particular item code