Re: Optimization question: Unrolling subquery into IN clause
Date: Fri, 16 Oct 2009 12:41:35 +0200
In article <Xns9CA6680BD4E25wrgrpde_at_news.albasani.net>, wr_at_spam.la says...
> I have a query that looks roughly like this:
> SELECT several_columns
> FROM tab1
> WHERE col1='Value'
> AND col2 IN
> SELECT key
> FROM tab2
> WHERE tab2.col3='Something'
Have you tried rewriting to:
SELECT key FROM tab2 WHERE tab2.col3='Something' AND tab1.col2=tab2.key
I do not recall the exact details but there is a class of queries where IN() is more efficient and another class where EXISTS() is more efficient even though you would hope Oracle could figure that out itself. Received on Fri Oct 16 2009 - 05:41:35 CDT