Обсуждение: NULLIF problem

HELLO,<br /><br />I encounter an error if i use NULLIF with timestamp with time zone.<br />eq.
dbtime=nullif(mytime,'')<br/><br />i want to null the value of field DBTIME if the variable mytime=" "<br /><br
/>DBTIME="timestamp with time zone" datatype <br /><br />error: column DBTIME is of type timestamp with time zone but
expressionis of type text.<br /><br />What should i do?<br /><br />Thanks in advance...<br clear="all" /><br />-- <br
/>GeraMel E. Handumon<br />Application Programmer <br />PaySoft Solutions, Inc.<br
/>-----------------------------------------------------------------<br/>"Share your knowledge. It's a way to achieve
immortality"- Dalai Lama  

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

On Nov 27, 2007, at 8:47 PM, Michael Glaesemann wrote:

>
> 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


Why not just:

UPDATE table
SET mytime=NULL
WHERE mytime='';

Erik Jones

Software Developer | Emma®
erik@myemma.com
800.595.4401 or 615.292.5888
615.292.0777 (fax)

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On Nov 28, 2007, at 14:00 , Erik Jones wrote:

> Why not just:
>
> UPDATE table
> SET mytime=NULL
> WHERE mytime='';

If mytime is a timestamp field, it won't have any values ''. I  
believe the OP is updating mytime to a client-supplied value which is  
passing '' when it probably means NULL.

Michael Glaesemann
grzm seespotcode net