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Re: Performance effect of number of columns on SELECT clause?

From: Connor McDonald <connor_mcdonald_at_yahoo.com>
Date: Wed, 27 Feb 2002 22:12:21 +0000
Message-ID: <3C7D59C5.1892@yahoo.com>


Pasi Kovanen wrote:
>
> We did some tests using different SELECT clauses and were
> surprised to found how much the number of columns that
> were selected affect the performance.
>
> For example, execution time of
> SELECT column1 from foobar
> seems to be almost constant whatever the size of data returned in
> column1 is 20 - 400 bytes (only 5% decrease w/ 400 bytes).
>
> Wheres
> SELECT column1, column2, ... column13 from foobar can take
> even 40% longer though mo

Is perhaps column1 indexed ? Try it with

SQL> set autotrace on

and see if you get the same explain plan for each.

hth
connor

-- 
==============================
Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."
Received on Wed Feb 27 2002 - 16:12:21 CST

Original text of this message

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