I've got a table called PRODUCT in an 8173 database as follows:

Name Null? Type
---------------------------------------- -------- ----------------------------
PRODUCT_ID NOT NULL VARCHAR2(8)
PRODUCT_DESC NOT NULL VARCHAR2(255)
NOMINAL_CODE NUMBER
PRODUCT_TYPE NUMBER(3)
UNIT_OF_MEASURE VARCHAR2(5)
QUANTITY NUMBER(12,2)
LAST_UPDATE DATE
PRODUCT_SHORT_DESC VARCHAR2(30)
EDI_PRODUCT_ID VARCHAR2(6)
SPS_PRODUCT_ID VARCHAR2(3)
TXU_PRODUCT_ID NOT NULL NUMBER

We have a developer that wants to add a column LOSSES_PRODUCT_ID that has a check constraint that says "if not null then must exist in product.product_id"
Is this possible - if so I'm not sure how to code it. Ahy help appreciated!
Thanks,
Fraze