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* setting the where clause
@ 2009-06-10 12:19 johnf <jfabiani@yolo.com>
0 siblings, 2 replies; 4+ messages in thread
From: johnf @ 2009-06-10 12:19 UTC (permalink / raw)
To: pgsql-sql
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".
I wonder what you guys think. How might it effect performance?
--
John Fabiani
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: setting the where clause
@ 2009-06-10 14:19 Tom Lane <tgl@sss.pgh.pa.us>
parent: johnf <jfabiani@yolo.com>
1 sibling, 1 reply; 4+ messages in thread
From: Tom Lane @ 2009-06-10 14:19 UTC (permalink / raw)
To: johnf <jfabiani@yolo.com>; +Cc: pgsql-sql
johnf <jfabiani@yolo.com> writes:
> 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".
Whoever said that doesn't know what they're talking about. It's not
faster (because it forces an actual index probe to happen) and it's not
safer (what if one day that PK value exists?).
I'd personally go with "where false"; why not say what you mean rather
than forcing humans and computers to deduce that the condition is
constant false?
regards, tom lane
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: setting the where clause
@ 2009-06-10 15:13 Rob Sargent <robjsargent@gmail.com>
parent: Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 0 replies; 4+ messages in thread
From: Rob Sargent @ 2009-06-10 15:13 UTC (permalink / raw)
To: pgsql-sql
Tom Lane wrote:
> johnf <jfabiani@yolo.com> writes:
>
>> 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".
>>
>
> Whoever said that doesn't know what they're talking about. It's not
> faster (because it forces an actual index probe to happen) and it's not
> safer (what if one day that PK value exists?).
>
> I'd personally go with "where false"; why not say what you mean rather
> than forcing humans and computers to deduce that the condition is
> constant false?
>
> regards, tom lane
>
>
Of course you would do the world a favour if you wrote a client-side
clear-the-screen routine that didn't pester the net and the server
un-necessarily.
^ permalink raw reply [nested|flat] 4+ messages in thread
* Re: setting the where clause
@ 2009-06-12 12:33 Jasen Betts <jasen@xnet.co.nz>
parent: johnf <jfabiani@yolo.com>
1 sibling, 0 replies; 4+ messages in thread
From: Jasen Betts @ 2009-06-12 12:33 UTC (permalink / raw)
To: pgsql-sql
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)
^ permalink raw reply [nested|flat] 4+ messages in thread
end of thread, other threads:[~2009-06-12 12:33 UTC | newest]
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-- links below jump to the message on this page --
2009-06-10 12:19 setting the where clause johnf <jfabiani@yolo.com>
2009-06-10 14:19 ` Tom Lane <tgl@sss.pgh.pa.us>
2009-06-10 15:13 ` Rob Sargent <robjsargent@gmail.com>
2009-06-12 12:33 ` Jasen Betts <jasen@xnet.co.nz>
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