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Re: Outer Join Performance

From: Dave Wotton <Dave.Wotton_at_dwotton.nospam.clara.co.uk>
Date: Fri, 26 Mar 1999 07:03:36 GMT
Message-ID: <cjGK2.37576$Eb.5506@nnrp2.clara.net>

Julia Cristina Varela de Montoya wrote in message <7dev3g$6gr$1_at_bgtnsc01.worldnet.att.net>...
>Our directors are under the assumption that outer-joins cause a performance
>decrease, and have instructed me to remove them from various places in
code,
>regardless of the fact that fewer rows may return.
>
>After doing explain plans, I see that outer-joins have less execution
steps,
>and do in fact return rows faster. Can someone summarize for me what I can
>say to management, or am I dreaming?

You cannot just eliminate outer-joins, they serve a specific need that normal joins cannot satisfy. I suppose it's possible that some careless programmers have used outer-joins where normal joins would have been perfectly acceptable, but the performance difference is absolutely minimal.

However, there are cases where outer-joins to views can be very expensive. I have written a paper on this, it's at:

         http://home.clara.net/dwotton/dba/ojoin2.htm

HTH, Dave.
--
Remove "nospam" from my address to reply by email Received on Fri Mar 26 1999 - 01:03:36 CST

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