The problem is that your subselect is not correlated. In other words, you need to join sp in the main query to supplier in the subquery -- don't join the tables in the subquery. Specifically, the query should be:

SELECT *
FROM sp
WHERE NOT EXISTS (
    SELECT 1
    FROM supplier     -- note SP doesn't appear here!
    WHERE supplier.num = sp.num  -- sp is from main query
)

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I wrote the same thing in my reply below, but didn't point it out specifically.

Do not rebuke them with harsh words ... but rather lead them gently - with URLs - so that they may learn wisdom.

In reply to Re^4: nested dbi queries question by VSarkiss
in thread nested dbi queries question by philosophia

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