Re: comparing null value in plpgsql. - Mailing list pgsql-bugs

On Mar 10, Stephan Szabo wrote:

> On Mon, 11 Mar 2002, Bhuvan A wrote:
>
> > here i have a problem in comparing null values in plpgsql. this exist
> > in 7.1.x and 7.2 as well.
> >
> > the condition <null value> != <valid value> fails in plpgsql.
> > consider this function is triggered on every updation on a table.
> >
> >   create function ftest()
> >   returns opaque as 'declare
> >
> >   begin
> >
> >     if new.comp_code != old.comp_code then
> >       ...
> >     end if;
> >     return new;
> >   end;'
> >   language 'plpgsql';
> >
> > this condition fails if old.comp_code is null and new.comp_code has
> > some value.
>
> <nullvalue> != <anything> is not true, it's unknown, so the if shouldn't

  what do you mean by <nullvalue> != <anything>?

> fire.  It's a side effect of how the spec defines operations on nulls.
>

here i mean..

if <nullvalue> != <not null value>, the loop is not fired. why?