Question

It’s a simple question, I’m getting started with SQL and I’m having a lot of problems with it.

I have TBL_SALES and TBL_CUSTOMERS. Both can be JOINed by the field CUSTOMER_ID.
A customer may have a CUSTOMER_ID and have no entry on TBL_CUSTOMERS

I would like to FITER all entries on TBL_SALES that don’t have an entry on TBL_CUSTOMERS.

Which I think it’s the opposite of

SELECT UNIQUE TBL_SALES.CUSTOMER_ID, TBL_CUSTOMERS.CUSTOMER_ID
FROM TBL_SALES, TBL_CUSTOMERS
WHERE TBL_SALES.CUSTOMER_ID = TBL_CUSTOMERS.CUSTOMER_ID

Well… I can do that with a VBA code using SEEK and NOMATCH. But I know it’s not productive. And if I try to use this code, it doesn’t work:

SELECT UNIQUE TBL_SALES.CUSTOMER_ID, TBL_CUSTOMERS.CUSTOMER_ID
FROM TBL_SALES, TBL_CUSTOMERS
WHERE TBL_SALES.CUSTOMER_ID <> TBL_CUSTOMERS.CUSTOMER_ID

I realized that there must be a ‘SEEK’ command in SQL but I’m pretty sure that is a smarter way to run this query.

Answer 1

Try

SELECT *
FROM TBL_SALES
WHERE NOT EXISTS
(SELECT * FROM TBL_CUSTOMERS
WHERE TBL_CUSTOMERS.CUSTOMER_ID = TBL_SALES.CUSTOMER_ID)

It’s also possible to use a LEFT JOIN, which selects all records on “the left” regardless wether or not there are existing records “on the right”.

SELECT *
FROM TBL_SALES LEFT JOIN TBL_CUSTOMERS
ON TBL_SALES.CUSTOMER_ID = TBL_CUSTOMERS.CUSTOMER_ID
WHERE TBL_CUSTOMERS.CUSTOMER_ID IS NULL