Re: SELECT x FROM DUAL is bad for system performance?

From: Connor McDonald <hamcdc_at_yahoo.co.uk>
Date: Thu, 13 Dec 2001 09:37:31 -0800
Message-ID: <F001.003DBFBA.20011213084030@fatcity.com>

I thinks it more that people often use it where it is not required. For example, they'll code (in PL/SQL)

select some_expression
into variable
from dual

instead of

variable := some_expression;

The other side of the equation is excessive use of SYSDATE or USER in PL/SQL, because x := sysdate; is converted to 'select sysdate into x from dual'

hth
connor

• Thomas Jeff <ThomasJe_at_tce.com> wrote: > On page 92 of Oracle Performance Tuning 101, there's
  > a recommendation
  > to avoid the use of SELECT X FROM DUAL, claiming
  > that it can '..use up
  > system
  > performance in a hurry', but does not go on to
  > elaborate as to exactly
  > *why*.
  >
  > Could someone shed a bit more light on this?
  > Thanks.
  >
  > --------------------------------------------
  > Jeffery D Thomas
  > DBA
  > Thomson Information Services
  > Thomson multimedia Inc.
  >
  > Email: thomasje_at_tce.com
  > DBA Quickplace: http://gkmqp.tce.com/tis_dba
  > --------------------------------------------
  >
  >
  >
  

  ---

Connor McDonald
http://www.oracledba.co.uk (mirrored at http://www.oradba.freeserve.co.uk)

"Some days you're the pigeon, some days you're the statue"

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Received on Thu Dec 13 2001 - 11:37:31 CST