Why UPDATE does not see result of subquery? [Oracle] - database

Question

After this query updated 0 rows:
UPDATE F_ANSWER fa
SET fa.STATUS_ID = 5
WHERE fa.ANSWER_ID IN (SELECT FA1.ANSWER_ID
FROM F_ANSWER FA1
WHERE FA1.ANSWER_ID = (SELECT ANSWER_ID
FROM F_ANSWER FA2
WHERE FA2.QUERY_ID = FA1.QUERY_ID
ORDER BY ANSWER_ID DESC
FETCH FIRST ROW ONLY)
);
but separately SELECT returned 2 rows with ID:
SELECT FA1.ANSWER_ID
FROM F_ANSWER FA1
WHERE FA1.ANSWER_ID = (SELECT ANSWER_ID FROM F_ANSWER FA2
Why is that?
Simplified subquery without link from subquery to query works fine:
UPDATE F_ANSWER fa
SET fa.STATUS_ID = 5
WHERE fa.ANSWER_ID IN (SELECT FA1.ANSWER_ID
FROM F_ANSWER FA1
WHERE FA1.ANSWER_ID = (SELECT ANSWER_ID
FROM F_ANSWER FA2
ORDER BY ANSWER_ID DESC
FETCH FIRST ROW ONLY)
);
I can resolve my problem with 2 queries - 1 for selecting necessary IDS and 2 for updating.
But it's interesting why update cannot see result of subquery with this structure.

Answer 1

You written two different update-query options: (1) one is written with a correlated subquery, and the other(2) just with a subquery.
I believe, that your data is such that the predicate in upd-query (1)
WHERE FA1.ANSWER_ID = (SELECT ANSWER_ID
FROM F_ANSWER FA2
WHERE FA2.QUERY_ID =
FA1.QUERY_ID
ORDER BY ANSWER_ID DESC
FETCH FIRST ROW ONLY)
cuts off the data.
in your main update query this block is a correlated subquery
UPDATE F_ANSWER fa
SET fa.STATUS_ID = 5
WHERE fa.ANSWER_ID IN (SELECT FA1.ANSWER_ID
FROM F_ANSWER FA1
WHERE FA1.ANSWER_ID = (SELECT ANSWER_ID
FROM F_ANSWER FA2
WHERE FA2.QUERY_ID =
FA1.QUERY_ID
ORDER BY ANSWER_ID DESC
FETCH FIRST ROW ONLY)
);
in this query, you are using a subquery without correlating by QUERY_ID(
....
WHERE FA2.QUERY_ID = FA1.QUERY_ID
....
):
UPDATE F_ANSWER fa
SET fa.STATUS_ID = 5
WHERE fa.ANSWER_ID IN (SELECT FA1.ANSWER_ID
FROM F_ANSWER FA1
WHERE FA1.ANSWER_ID = (SELECT ANSWER_ID
FROM F_ANSWER FA2
ORDER BY ANSWER_ID DESC
FETCH FIRST ROW ONLY)
);
You can provide an example of your data and formulate your task.
Your UPD-query can be rewritten an easier.