Обсуждение: Little Suggestion for 6.6
I don't know what SQL standards say about this, but in: tacacs=> SELECT * FROM users,counters WHERE users.username=counters.username AND username='foobar'; ERROR: Column 'username' is ambiguous ...username is NOT ambiguous... Bye! -- Daniele -------------------------------------------------------------------------------Daniele Orlandi - Utility Line Italia - http://www.orlandi.comViaMezzera 29/A - 20030 - Seveso (MI) - Italy -------------------------------------------------------------------------------
> > I don't know what SQL standards say about this, but in: > > tacacs=> SELECT * FROM users,counters WHERE > users.username=counters.username AND username='foobar'; ERROR: > Column 'username' is ambiguous > > ...username is NOT ambiguous... I don't believe you. -- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
On Wed, 30 Jun 1999, Daniele Orlandi wrote:
>
> I don't know what SQL standards say about this, but in:
>
> tacacs=> SELECT * FROM users,counters WHERE users.username=counters.username AND
> username='foobar';
> ERROR: Column 'username' is ambiguous
>
> ...username is NOT ambiguous...
Of course it is...which username do you want to match on, users.username
or counters.username?
Marc G. Fournier ICQ#7615664 IRC Nick: Scrappy
Systems Administrator @ hub.org
primary: scrappy@hub.org secondary: scrappy@{freebsd|postgresql}.org
The Hermit Hacker wrote: > > > tacacs=> SELECT * FROM users,counters WHERE users.username=counters.username > > AND username='foobar'; > > ERROR: Column 'username' is ambiguous > > > > ...username is NOT ambiguous... > > Of course it is...which username do you want to match on, users.username > or counters.username? IMHO it's the same, since they have to be equal... Pardon me if I'm not seeing something obvious :^) Bye. -- Daniele -------------------------------------------------------------------------------Daniele Orlandi - Utility Line Italia - http://www.orlandi.comViaMezzera 29/A - 20030 - Seveso (MI) - Italy -------------------------------------------------------------------------------
At 08:56 PM 6/29/99 -0300, The Hermit Hacker wrote: >On Wed, 30 Jun 1999, Daniele Orlandi wrote: > >> >> I don't know what SQL standards say about this, but in: >> >> tacacs=> SELECT * FROM users,counters WHERE users.username=counters.username AND >> username='foobar'; >> ERROR: Column 'username' is ambiguous >> >> ...username is NOT ambiguous... >Of course it is...which username do you want to match on, users.username >or counters.username? He's saying that the expression can be resolved because their values are equal, so it doesn't matter which username you match on. Which means he thinks that expression semantics rather than scoping/parsing/type rules ought to determine what is and what is not an ambiguous expression. Which is...well... just wrong :) - Don Baccus, Portland OR <dhogaza@pacifier.com> Nature photos, on-line guides, and other goodies at http://donb.photo.net
On Wed, 30 Jun 1999, Daniele Orlandi wrote:
>
>
> The Hermit Hacker wrote:
> >
> > > tacacs=> SELECT * FROM users,counters WHERE users.username=counters.username
> > > AND username='foobar';
> > > ERROR: Column 'username' is ambiguous
> > >
> > > ...username is NOT ambiguous...
> >
> > Of course it is...which username do you want to match on, users.username
> > or counters.username?
>
> IMHO it's the same, since they have to be equal...
>
> Pardon me if I'm not seeing something obvious :^)
If I understand things (which could be pushing it), the join that is being
attempted (simplistically) gets broken down as something like:
a) find all usernames in users that exist in counters
b) find all usernames in ?? that equals foobar
c) find all a AND b
Very simplistic, mind you...
IN the above sample, b can't be resolved, since you don't tell it which
table to search for the username...
Marc G. Fournier ICQ#7615664 IRC Nick: Scrappy
Systems Administrator @ hub.org
primary: scrappy@hub.org secondary: scrappy@{freebsd|postgresql}.org