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From: Michael Glaesemann <grzm@seespotcode.net>
Subject: Re: NULLIF problem
Date: Tue, 27 Nov 2007 21:47:36 -0500
To: "Gera Mel Handumon" <geramel.h@gmail.com>


On Nov 27, 2007, at 21:04 , Gera Mel Handumon wrote:

> I encounter an error if i use NULLIF with timestamp with time zone.
> eq. dbtime=nullif(mytime,'')
>
> i want to null the value of field DBTIME if the variable mytime=" "
>
> DBTIME ="timestamp with time zone" datatype
>
> error: column DBTIME is of type timestamp with time zone but  
> expression is of type text.

I believe the reason is that '' is not a valid timestamp value: think  
of it this way:

IF mytime = '' THEN
   mytime := NULL;
END IF;

The first thing it needs to do is compare the mytime value with ''.  
As '' is not a valid timestamp value, it may be casing mytime to  
text. You'll run into problems if you're assigning a text value to a  
timestamp field (which happens after the initial comparison--and the  
cast--are done.)

I think you may need to handle this is you middleware, or handle the  
IF THEN explicitly in a function. Maybe CASE would work:

CASE WHEN mytime = '' THEN NULL
      ELSE CAST(mytime AS TIMESTAMP)
     END

Michael Glaesemann
grzm seespotcode net