Thread: CREATE TABLE docs fix
This patch fixes a minor inaccuracy in the documentation: NOT NULL is not synonymous with CHECK (xxx IS NOT NULL) -- for example, consider ALTER TABLE ADD PRIMARY KEY, which checks for 'NOT NULL', not a check constraint. Cheers, Neil -- Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC
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On Sun, 2002-09-01 at 04:00, Neil Conway wrote: > This patch fixes a minor inaccuracy in the documentation: NOT NULL is > not synonymous with CHECK (xxx IS NOT NULL) -- for example, consider > ALTER TABLE ADD PRIMARY KEY, which checks for 'NOT NULL', not a check > constraint. Yeah, but they're still synonymous.
Rod Taylor <rbt@zort.ca> writes: > On Sun, 2002-09-01 at 04:00, Neil Conway wrote: > > This patch fixes a minor inaccuracy in the documentation: NOT NULL > > is not synonymous with CHECK (xxx IS NOT NULL) -- for example, > > consider ALTER TABLE ADD PRIMARY KEY, which checks for 'NOT NULL', > > not a check constraint. > > Yeah, but they're still synonymous. How so? Their behavior is clearly different (note the case above, as well as any other situation in which the system attempts to determine if a column allows a NULL value). Since they are not interchangeable, they can't be synonyms. Cheers, Neil -- Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC
On Sun, 2002-09-01 at 13:28, Neil Conway wrote: > Rod Taylor <rbt@zort.ca> writes: > > > On Sun, 2002-09-01 at 04:00, Neil Conway wrote: > > > This patch fixes a minor inaccuracy in the documentation: NOT NULL > > > is not synonymous with CHECK (xxx IS NOT NULL) -- for example, > > > consider ALTER TABLE ADD PRIMARY KEY, which checks for 'NOT NULL', > > > not a check constraint. > > > > Yeah, but they're still synonymous. > > How so? Their behavior is clearly different (note the case above, as > well as any other situation in which the system attempts to determine > if a column allows a NULL value). > > Since they are not interchangeable, they can't be synonyms. The case you brought up is more of a bug or mis-implementation of alter table / add primary key. I guess you're right. They're not, but they should be.
En 01 Sep 2002 13:44:37 -0400 Rod Taylor <rbt@zort.ca> escribió: > > > On Sun, 2002-09-01 at 04:00, Neil Conway wrote: > > > > This patch fixes a minor inaccuracy in the documentation: NOT NULL > > > > is not synonymous with CHECK (xxx IS NOT NULL) -- for example, > > > > consider ALTER TABLE ADD PRIMARY KEY, which checks for 'NOT NULL', > > > > not a check constraint. > > The case you brought up is more of a bug or mis-implementation of alter > table / add primary key. I guess you're right. They're not, but they > should be. I think it's very difficult in the general case to determine from a CHECK constraint if it is setting some column to not null; but if it was easy, then you better translate(*) it into the SET NOT NULL form, and leave the ADD PRIMARY KEY code alone. Anyway IMHO this should be documented to prevent possible confusion. (*) but I think auto-converting some things into some other things that may not be what the user wants is a recipe for user frustration. -- Alvaro Herrera (<alvherre[a]atentus.com>) "El sabio habla porque tiene algo que decir; el tonto, porque tiene que decir algo" (Platon).
Is this patch to be applied? --------------------------------------------------------------------------- Neil Conway wrote: > This patch fixes a minor inaccuracy in the documentation: NOT NULL is > not synonymous with CHECK (xxx IS NOT NULL) -- for example, consider > ALTER TABLE ADD PRIMARY KEY, which checks for 'NOT NULL', not a check > constraint. > > Cheers, > > Neil > > -- > Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC [ Attachment, skipping... ] > > ---------------------------(end of broadcast)--------------------------- > TIP 5: Have you checked our extensive FAQ? > > http://www.postgresql.org/users-lounge/docs/faq.html -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 Index: doc/src/sgml/ref/create_table.sgml =================================================================== RCS file: /var/lib/cvs/pgsql-server/doc/src/sgml/ref/create_table.sgml,v retrieving revision 1.55 diff -c -r1.55 create_table.sgml *** doc/src/sgml/ref/create_table.sgml 18 May 2002 15:44:47 -0000 1.55 --- doc/src/sgml/ref/create_table.sgml 1 Sep 2002 07:52:51 -0000 *************** *** 247,255 **** <term><literal>NOT NULL</></term> <listitem> <para> ! The column is not allowed to contain NULL values. This is ! equivalent to the column constraint <literal>CHECK (<replaceable ! class="PARAMETER">column</replaceable> NOT NULL)</literal>. </para> </listitem> </varlistentry> --- 247,253 ---- <term><literal>NOT NULL</></term> <listitem> <para> ! The column is not allowed to contain NULL values. </para> </listitem> </varlistentry>
Bruce Momjian <pgman@candle.pha.pa.us> writes: > Is this patch to be applied? Yes, IMHO anyway. Cheers, Neil -- Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC
Your patch has been added to the PostgreSQL unapplied patches list at:
http://207.106.42.251/cgi-bin/pgpatches
I will try to apply it within the next 48 hours.
---------------------------------------------------------------------------
Neil Conway wrote:
> This patch fixes a minor inaccuracy in the documentation: NOT NULL is
> not synonymous with CHECK (xxx IS NOT NULL) -- for example, consider
> ALTER TABLE ADD PRIMARY KEY, which checks for 'NOT NULL', not a check
> constraint.
>
> Cheers,
>
> Neil
>
> --
> Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC
[ Attachment, skipping... ]
>
> ---------------------------(end of broadcast)---------------------------
> TIP 5: Have you checked our extensive FAQ?
>
> http://www.postgresql.org/users-lounge/docs/faq.html
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
Patch applied. Thanks. --------------------------------------------------------------------------- Neil Conway wrote: > This patch fixes a minor inaccuracy in the documentation: NOT NULL is > not synonymous with CHECK (xxx IS NOT NULL) -- for example, consider > ALTER TABLE ADD PRIMARY KEY, which checks for 'NOT NULL', not a check > constraint. > > Cheers, > > Neil > > -- > Neil Conway <neilc@samurai.com> || PGP Key ID: DB3C29FC [ Attachment, skipping... ] > > ---------------------------(end of broadcast)--------------------------- > TIP 5: Have you checked our extensive FAQ? > > http://www.postgresql.org/users-lounge/docs/faq.html -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073