Subject Re: [firebird-support] Comparing two tables and locate not matched question
Author
Jim
Not sure from your question which table should be first, but wouldn't something like this work for you if
either Active_Inventory.product_ID was a Primary Key or both tables have a unique index on this field?

SELECT a.product_ID, b.product_ID 
FROM Active_Inventory a 
LEFT JOIN Vendor_Products b ON a.product_ID = b.product_ID
WHERE b.product_ID IS NULL