thanks for your quick reply sasha

my 2 tables have similar fields. the only difference is that sales
invoice table have field duedate.

SALES_INVOICE:
ID
CODE
POSTDATE
DUEDATE
CUSTOMER_ID
AMOUNT
STATUS


CREDIT_MEMO:
ID
CODE
POSTDATE
CUSTOMER_ID
AMOUNT
STATUS


yes i'd like to union this tables. but is it possible to know if the
record comes from which table?