Plea for Query Tuning Help

From: Charlotte Hammond <charlottejanehammond_at_yahoo.com>
Date: Tue, 12 Sep 2006 09:10:38 -0700 (PDT)
Message-ID: <20060912161038.51602.qmail@web34107.mail.mud.yahoo.com>

Hi all,

I have a very complicated view, NASTY_VIEW.

SELECT *
FROM NASTY_VIEW
WHERE ID = :bind

This is fast (< 1 second). CBO cost = 400. Fantastic.

However if I try

SELECT *
FROM NASTY_VIEW
WHERE ID = (SELECT id FROM my_table WHERE ROWNUM=1)

This takes "forever" (well >> hours). my_table is a simple table and id is the primary key. CBO cost = 22000. Not fantastic. (SELECT id FROM my_table WHERE ROWNUM=1) happens in the blink of an eye if run alone.

The execution plans are very different and it looks as if Oracle has attempted to merge the subquery into the top-level select. Similar things happen if I use a join instead of a sub-query.

How can I prevent this happening so that it "looks" like the first "fantastic" query? I've tried messing with hints (NO_MERGE and PUSH_SUBQ) but I don't know enough to do so effectively. Statistics are full and up to date. This is Oracle 9.2.0.6.

Any suggestions would be greatfully received!

Thank you
Charlotte

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Received on Tue Sep 12 2006 - 11:10:38 CDT