From: Bruce Momjian <pgman@candle.pha.pa.us>
Message-Id: <200502110432.j1B4W5M02420@candle.pha.pa.us>
Subject: Re: Default Values Section
In-Reply-To: <009401c4f286$01cc6b50$fc00a8c0@hermes>
To: Lourival Oliveira <lourival@lourival.eti.br>
Date: Thu, 10 Feb 2005 23:32:05 -0500 (EST)
Cc: pgsql-docs@postgresql.org
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OK, I updated the documentation to add a comment on that line:
	
	SELECT CURRENT_TIMESTAMP;
	SELECT now();
	SELECT TIMESTAMP 'now';  -- incorrect for use with DEFAULT


---------------------------------------------------------------------------

Lourival Oliveira wrote:
> I have a problem reading the "5.3 Default Values" Section of 
> Postgresql8.0.0-rc1 documentation. In this section there are nothing about 
> using 'now' constant. I think which there are a conflict with a note about 
> 'now' in section "9.9. Date/Time Functions and Operators" which show the way 
> to achieve the desired behavior. See:
> 
> 5.3. Default Values
> 
> ...
> 
> The default value may be a scalar expression, which will be evaluated 
> whenever the default value is inserted (not when the table is created).
> 
> 
> 9.9. Date/Time Functions and Operators
> 
> ...
> 
> SELECT CURRENT_TIMESTAMP;
> SELECT now();
> SELECT TIMESTAMP 'now';
> Note: You do not want to use the third form when specifying a DEFAULT clause 
> while creating a table. The system will convert now to a timestamp as soon 
> as the constant is parsed, so that when the default value is needed, the 
> time of the table creation would be used! The first two forms will not be 
> evaluated until the default value is used, because they are function calls. 
> Thus they will give the desired behavior of defaulting to the time of row 
> insertion.
> 
> I think which a simple reference to any unpredictable behavior must be 
> placed here to avoid confusion when anybody don't reach the desired behavior 
> when use default values.
> 
> What think you about my suggestion?
> 
> Wait replies, Tanks.
> 
> Lourival Oliveira da Silva
> 
> PS: Sorry by my poor English. 
> 
> 
> 
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