Joining two resident tables

[#1]

I have tow tables with information of which I want to multiply a value from table 1 with a value from table 2 and store it in table 3.

First table

%ITM , TTYPE, TQTY

Second table

DOCO, %ITM, QTY

I want to multiply QTY with TQTY and store this in a third table

table 3

DOCO, SERVICE, SCOST

Second.DOCO = DOCO

first.TTYPE = SERVICE

TQTY.QTY = SCOST

I dont know how to load info from 2 resident tables.

Who can help me