To: pgsql-sql@postgresql.org
Path: not-for-mail
From: Jasen Betts <jasen@xnet.co.nz>
Newsgroups: gmane.comp.db.postgresql.sql
Subject: Re: setting the where clause
Date: 12 Jun 2009 12:33:28 GMT
Organization: Dis (not Dat) Organisation
Lines: 27
Message-ID: <h0thuo$38v$1@reversiblemaps.ath.cx>
References: <200906100519.34171.jfabiani@yolo.com>
NNTP-Posting-Host: localhost
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
User-Agent: slrn/pre1.0.0-2 (Linux)

On 2009-06-10, johnf <jfabiani@yolo.com> wrote:
> Hi,
> I'm am programming in python using the Dabo modules.  www.dabodev.com if your 
> interested.  Dabo is a framework that provides an easy way to build desktop 
> app's.  To clear a data entry form. I have been setting the where clause 
> to "where 1=0".  This of course retrieves 0 records and my form will display 
> nothing.  It has been suggested that it might be better to set the where 
> clause to a primary key value that does not exist in the table  "where PK 
>= -9999999".   

"where PK=NULL" is better as anything=NULL is never true. PK=-9999999
may be true sometimes.

As Tom says  PK=-9999999  causes postgres to look for a record that
matches, PK=NULL doesn't cause needless search.

that said if -9999999 is outside of the valid range for PK then the
search will finish very quickly as at worst only a sigle btree page
will need to be loaded.

in order of preference.

  no query at all
  where FALSE
  where PK=NULL
  where PK=-9999999 (note that this one may not work)