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Re: Major upgrade advice

From: Roberto Garcia <roberto(dot)garcia(at)cptec(dot)inpe(dot)br>
To: Achilleas Mantzios <achill(at)matrix(dot)gatewaynet(dot)com>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: Major upgrade advice
Date: 2008-06-20 13:26:19
Message-ID: 485BAFFB.80300@cptec.inpe.br (view raw or flat)
Thread:
Lists: pgsql-admin
We have an index on the time_stamp column, if the format of argument is 
different from the format the index was created it is not used, then 
performance is decreased because a sequential scan is done instead of an 
index scan.

Achilleas Mantzios wrote:
> Why not simply,
> SELECT * FROM xxx WHERE <timestamp_column>::date = '2008-05-20'::date;
>
> Στις Thursday 19 June 2008 21:56:09 ο/η Roberto Garcia έγραψε:
>   
>> We changed it because 8.3 doesn't allow the operator LIKE on timestamp 
>> columns. Your syntax works fine but we weren't used to use as u do. 
>> There weren't any specific reason, only another way to do that.
>>
>> I think when we read that operator LIKE and timestamp values were 
>> incompatible we assumed that timestamp values couldn't be compared to 
>> any char value, opposed as your syntax is.
>>
>> We've tried to do "select * from X where <timestamp column> = 
>> '2008-05-20 10:'", expecting that the result would be any minute from 10 
>> o'clock (10:15, 10:30, 10:45, etc) of the specific date, but this syntax 
>> retrieves only 10:00 from that date.
>>
>> Tks for the new syntax.
>>
>> Regards
>> Roberto Garcia
>>
>> Gregory S. Youngblood wrote:
>>     
>>> That's a pretty substantial change.  Why did you have to make this change?
>>> Was it causing syntax errors or to get better performance on those types of
>>> queries? Actually, now that I think about it, didn't:
>>> select * from X where <timestamp column> between '2008-05-20 00:00:00' and
>>> '2008-05-20 23:59:59' 
>>> work? I could have sworn I have used that syntax in 8.2 without having to
>>> arbitrarily cast the arguments... now I'm going to have to go look. :)
>>>
>>> Yup, confirmed, 8.2.7 and no casting on the date arguments when I was using
>>> between.
>>>
>>> I'm just curious if there was a specific reason (i.e. better performance,
>>> better use of indexes, etc.) for your syntax.
>>>
>>> Thanks,
>>> Greg
>>>
>>> -----Original Message-----
>>> From: pgsql-admin-owner(at)postgresql(dot)org
>>> [mailto:pgsql-admin-owner(at)postgresql(dot)org] On Behalf Of Roberto Garcia
>>> Sent: Wednesday, June 18, 2008 12:01 PM
>>> Cc: pgsql-admin(at)postgresql(dot)org
>>> Subject: Re: [ADMIN] Major upgrade advice
>>>
>>> Just to mention one issue we had here:
>>>
>>> In 8.1 we did this to retrieve all data from a specific date:
>>> SELECT * FROM xxx
>>> WHERE <timestamp_column> LIKE '2008-05-20%'
>>>
>>> In 8.3 we had to change to:
>>> SELECT * FROM xxx
>>> WHERE <timestamp_column> >= CAST('2008-05-20' as timestamp) AND
>>>       <timestamp_column> < CAST('2008-05-21' as timestamp)
>>>
>>> Regards
>>> Roberto Garcia
>>>
>>>
>>>   
>>>       
>> Roberto Garcia
>> Banco de Dados, MSc
>> Fone: (12) 3186-8405 
>> -- 
>> A luta contra o aquecimento global depende de cada um de nós, faça sua parte, economize recursos naturais.
>> -- 
>> http://www.cptec.inpe.br
>> http://www.inpe.br 
>>
>>
>>     
>
>
>
>   


Roberto Garcia
Banco de Dados, MSc
Fone: (12) 3186-8405 
-- 
A luta contra o aquecimento global depende de cada um de nós, faça sua parte, economize recursos naturais.
-- 
http://www.cptec.inpe.br
http://www.inpe.br 


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