ORA-01799: a column may not be outer-joined to a subquery

Question

Here is my query

SELECT 
    COUNT(C.SETID)
FROM 
    MYCUSTOMER C
    LEFT OUTER JOIN MYCUSTOPTION CO 
    ON 
        (C.SETID = CO.SETID 
            AND          


        

Answer 1

Well, Oracle apparently doesn't support using a subquery inside the join condition for an outer join. So you need to get rid of the subquery.

The question is, why is it there at all? You have "<=" conditions in two places, so the predicate essentially says "all records whose effective date is no later than the latest effective date that is no later than now". If that's what you really want, you could simplify it to "all records whose effective date is no later than now", i.e.:

ON 
    (C.SETID = CO.SETID 
        AND C.CUST_ID = CO.CUST_ID 
        AND CO.effdt <= SYSDATE    
)

Voila, no subquery.

But is that really what you want, or did you mean that first "<=" to be just "=" -- i.e. find the record with the most recent effective date before now? If that's what you really want, it will be more complex to rewrite.