Today I got a ticket from a developer where he claimed Oracle has a bug somewhere. The reason for this claim was a statement similar to
WHERE tab1col1 IN
( SELECT tab1col1
This query returned rows.
But when he run the inner query on it's own, he received
ORA-00904: "TAB1COL1": invalid identifier
00904. 00000 - "%s: invalid identifier"
as there is no column TAB1COL1 in TABLE2.
So why should there be any result for the full query when part of it fails already? Is oracle somehow ignoring the query on table2 totally due to some errors in optimization?
After some research and a 10053 trace (yes, it was not obvious for me) I saw Oracle doing a Cost‑based predicate pushdown (JPPD) and translates it to something like
AND EXISTS (SELECT 0 FROM "TABLE2" WHERE "TABLE1"."TAB1COL1"="TABLE1"."TAB1COL1")
With this hint (for me, not a /*+ syntax thing) it was obvious.
So my proposal was to be more specific and use alias like this:
FROM table1 t1
WHERE t1.tab1col1 IN
( SELECT t2.tab1col1
FROM table2 t2)
to generate the expected ORA-904