Обсуждение: no value fetch

hi,

Imagine that I have the following table where ts_sent is a timestamp(0)

select * from notification;
      to_used        | ts_sent                 |   from
---------------------+-------------------------+---------
 amanda@obs.unige.ch |  2004-07-21 14:19:43+02 | amanda
 amanda@obs.unige.ch |                         | postgres

and so, how do I do to fetch the second line by asking :
catch me the line where ts_sent doesn't have a value !

I've try:
select * from notification where ts_sent = null ;
without success...

Anyone has an idea how to do this ?

Thanks in advance !

Cedric BRINER

On Tue, 27 Jul 2004, BRINER Cedric wrote:

> hi,
>
> Imagine that I have the following table where ts_sent is a timestamp(0)
>
> select * from notification;
>       to_used        | ts_sent                 |   from
> ---------------------+-------------------------+---------
>  amanda@obs.unige.ch |  2004-07-21 14:19:43+02 | amanda
>  amanda@obs.unige.ch |                         | postgres
>
> and so, how do I do to fetch the second line by asking :
> catch me the line where ts_sent doesn't have a value !
>
> I've try:
> select * from notification where ts_sent = null ;

Use ts_sent IS NULL, not ts_sent = null.

Pretty much, <anything> = null returns null.

Stephan Szabo <sszabo@megazone.bigpanda.com> wrote:
>
>
> On Tue, 27 Jul 2004, BRINER Cedric wrote:
>
> > hi,
> >
> > Imagine that I have the following table where ts_sent is a timestamp(0)
> >
> > select * from notification;
> >       to_used        | ts_sent                 |   from
> > ---------------------+-------------------------+---------
> >  amanda@obs.unige.ch |  2004-07-21 14:19:43+02 | amanda
> >  amanda@obs.unige.ch |                         | postgres
> >
> > and so, how do I do to fetch the second line by asking :
> > catch me the line where ts_sent doesn't have a value !
> >
> > I've try:
> > select * from notification where ts_sent = null ;
>
> Use ts_sent IS NULL, not ts_sent = null.
>
> Pretty much, <anything> = null returns null.

To expand on this... This is because NULL is nothing.  Not zero, but
*nothing*.  Being nothing, it cannot "equal" anything.  Not even
itself.  But a space can *contain* nothing.  And it can contain "not
nothing."

Jim