Обсуждение: change null to ""

hi, all experts there,

it's me again :-)

I'm studying the example in postgresql-6.5.1/src/pl/plpgsql/test.
I have another question: why do we need to "Set backlink to empty string if
NULL value given"? is it JUST a test, or, some reasons to
do that in general?

Thanks!!!!!!!!!!!

amy

#################################################

-- ************************************************************
-- * BEFORE INSERT or UPDATE on all slots with backlink
-- *    - Set backlink to empty string if NULL value given
-- ************************************************************
create function tg_chkbacklink() returns opaque as '
begin
    if new.backlink isnull then
        new.backlink := '''';
    end if;
    return new;
end;
' language 'plpgsql';

create trigger tg_chkbacklink before insert or update
    on PSlot for each row execute procedure tg_chkbacklink();

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amy cheng wrote:
>
> hi, all experts there,
>
> it's me again :-)
oh well :)
> I'm studying the example in postgresql-6.5.1/src/pl/plpgsql/test.
> I have another question: why do we need to "Set backlink to empty string if
> NULL value given"? is it JUST a test, or, some reasons to
> do that in general?
Nope, it's just an example of "triggers".
You should also post the CREATE statement of PSlot,
does it have a "NOT NULL" constraint for backlink attribute?
if yes, you've got the answer (I would also have a look but
I'm on the other OS right now :> )

> -- ************************************************************
> -- * BEFORE INSERT or UPDATE on all slots with backlink
> -- *    - Set backlink to empty string if NULL value given
> -- ************************************************************
> create function tg_chkbacklink() returns opaque as '
> begin
>     if new.backlink isnull then
>         new.backlink := '''';
>     end if;
>     return new;
> end;
> ' language 'plpgsql';
>
> create trigger tg_chkbacklink before insert or update
>     on PSlot for each row execute procedure tg_chkbacklink();
>
> ______________________________________________________
> Get Your Private, Free Email at http://www.hotmail.com
>
> ************

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