Re: Trigger for modification timestamp column

2010/7/7 Johan Andersson <warb@mail.com>:
>
> 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?

sorry - it isn't possible - you cannot do it. You need one column more
for information if value is modified or not.

Regards

Pavel Stehule



>
> Thanks in advance!
>
> / Johan
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