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Re: JOIN vs. LEFT JOIN

From: Andreas Wenk <a(dot)wenk(at)netzmeister-st-pauli(dot)de>
To: Nico Callewaert <callewaert(dot)nico(at)telenet(dot)be>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: JOIN vs. LEFT JOIN
Date: 2009-01-28 13:00:26
Message-ID: 498056EA.3050102@netzmeister-st-pauli.de (view raw or flat)
Thread:
Lists: pgsql-novice
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Nico Callewaert schrieb:
> 
>> Ok please don't get me wrong for asking again: one customer can have
>> two tax rates? Why?
>> Because he's living in the USA and has a taxrate of 25% and lives also
>> in Germany and has
>> 19%? Hm ... strange ... ;-) . And also the custumer is 'prospect' OR
>> 'not active' ... but
>> not both ... ;-)
>>
>>> drop downs in the application, so the customer can easily select a
>>> value.
>>
>> So all these dropdowns are multiselect ...?
>>
>> I am not sure if I can help you with this. My idea is really to think
>> about the design of
>> the application and / or the database ... again - please don't get me
>> wrong ...
> 
> 
> Hi Andreas,
> 
> I think we are not understanding each other :-)

sometimes I am good with that ;-)

> It's al the time just 1 value, 1 value for tax, 1 value for customer
> type. No multiselect drop downs.  But all these fields are of course
> referencing a lookup table by ID.  But like Regina also said, the
> performance hit of the LEFT JOIN seems not worth considering putting
> junk data in the database that should be NULL (if the drop down is left
> blanc)...
> I don't know if I made myself clear ?

yes you did - don't worry. I have just another idea how I would do that. But anyway I
think the basic question was if a LEFT JOIN has less performance comparing with a JOIN. So
now we have the answer for your case and that hopefully helps you to get your software
work well.

In all cases EXPLAIN ANALYZE is a good idea to use ...

> Thanks !
> Nico
> 
Cheers

Andy

- --
St.Pauli - Hamburg - Germany

Andreas Wenk
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