Re: Trigger for modification timestamp column

2010/7/7 Susan Cassidy <scassidy(at)stbernard(dot)com>:
> Can't you check it using something like this:
>
> IF OLD.modified = NEW.modified THEN
>  NEW.modified = NOW();
> END IF;
> RETURN NEW;

but this take only case where column modified was changed. There are
not a functionality for detection if user explicitly updated column or
not

Pavel

>
> Susan
> -----Original Message-----
> From: pgsql-general-owner(at)postgresql(dot)org [mailto:pgsql-general-owner(at)postgresql(dot)org] On Behalf Of Johan Andersson
> Sent: Wednesday, July 07, 2010 6:49 AM
> To: pgsql-general(at)postgresql(dot)org
> Subject: [GENERAL] Trigger for modification timestamp column
>
>
> Hello!
>
> I am trying to write a trigger for updating a modification column and am
> having some trouble getting it to behave as I want.
>
> The trigger should set the column to the supplied value if it is set in the
> UPDATE statement and to the current timestamp [NOW()] if it is not. The
> problem is that I don't know how to check if the column is set or not. I can
> check the column's value for NULL but that doesn't work if I want the column
> to accept NULL values (meaning "unmodified").
>
> I would like something like:
> CREATE FUNCTION update_modified()
>    RETURNS TRIGGER AS $$
>        BEGIN
>            IF NOT isset(NEW.modified) THEN
>                NEW.modified = NOW();
>            END IF;
>            RETURN NEW;
>        END;
>    $$ LANGUAGE 'plpgsql';
>
> Does anyone know how to do this?
>
> Thanks in advance!
>
> / Johan
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>
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