Thread: generated constraint name

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/17/ddl-alter.html
Description:

url:
https://www.postgresql.org/docs/current/ddl-alter.html#DDL-ALTER-REMOVING-A-CONSTRAINT

(If you are dealing with a generated constraint name like $2, don't forget
that you'll need to double-quote it to make it a valid identifier.)

If I have a constraint with the name $2, are there other constraints with
names $1, $3 ... ?

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/17/ddl-alter.html
Description:

url:
https://www.postgresql.org/docs/current/ddl-alter.html#DDL-ALTER-REMOVING-A-CONSTRAINT

(If you are dealing with a generated constraint name like $2, don't forget
that you'll need to double-quote it to make it a valid identifier.)

If I have a constraint with the name $2, are there other constraints with
names $1, $3 ... ?

On Sunday, April 6, 2025, PG Doc comments form <noreply@postgresql.org> wrote:

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/17/ddl-alter.html
Description:

url:
https://www.postgresql.org/docs/current/ddl-alter.html#DDL-ALTER-REMOVING-A-CONSTRAINT

(If you are dealing with a generated constraint name like $2, don't forget
that you'll need to double-quote it to make it a valid identifier.)

If I have a constraint with the name $2, are there other constraints with
names $1, $3 ... ?

I feel like that whole parenthetical should just go away.  The point of the comment is to remind the user of how identifier values work with respect to mandatory double quoting.  The name itself, other than having a $, has no special importance.

David J.

On 07.04.25 15:34, David G. Johnston wrote:
> On Sunday, April 6, 2025, PG Doc comments form <noreply@postgresql.org 
> <mailto:noreply@postgresql.org>> wrote:
> 
>     The following documentation comment has been logged on the website:
> 
>     Page: https://www.postgresql.org/docs/17/ddl-alter.html <https://
>     www.postgresql.org/docs/17/ddl-alter.html>
>     Description:
> 
>     url:
>     https://www.postgresql.org/docs/current/ddl-alter.html#DDL-ALTER-
>     REMOVING-A-CONSTRAINT <https://www.postgresql.org/docs/current/ddl-
>     alter.html#DDL-ALTER-REMOVING-A-CONSTRAINT>
> 
>     (If you are dealing with a generated constraint name like $2, don't
>     forget
>     that you'll need to double-quote it to make it a valid identifier.)
> 
>     If I have a constraint with the name $2, are there other constraints
>     with
>     names $1, $3 ... ?
> 
> 
> I feel like that whole parenthetical should just go away.  The point of 
> the comment is to remind the user of how identifier values work with 
> respect to mandatory double quoting.  The name itself, other than having 
> a $, has no special importance.

I think generated constraint names were generally "$1", "$2", etc. at 
some point, instead of the more readable ones you get today.  But this 
must be ancient.

Peter Eisentraut <peter@eisentraut.org> writes:
> On 07.04.25 15:34, David G. Johnston wrote:
>> I feel like that whole parenthetical should just go away.  The point of 
>> the comment is to remind the user of how identifier values work with 
>> respect to mandatory double quoting.  The name itself, other than having 
>> a $, has no special importance.

> I think generated constraint names were generally "$1", "$2", etc. at 
> some point, instead of the more readable ones you get today.  But this 
> must be ancient.

Good point.  A bit of git-blame'ing shows that this documentation
wording appeared in e560dd353 of 2003-11-05, but we changed the
generation rule to not be "$n" in 45616f5bb of 2004-06-10.
(Oddly, I moved this documentation text around in 2005 without
noticing it was obsolete; or perhaps I did realize that but figured
it was still applicable to versions in the field.)

I concur with David that we should just drop the para.  It's merely
confusing now.  If you have a generated constraint name, it won't
require double-quoting unless your table or column name does, and
if they do you are doubtless already quite familiar with how
quoting works.

            regards, tom lane

Peter Eisentraut <peter@eisentraut.org> writes:

On 07.04.25 15:34, David G. Johnston wrote:

I feel like that whole parenthetical should just go away.  The point of

the comment is to remind the user of how identifier values work with

respect to mandatory double quoting.  The name itself, other than having

a $, has no special importance.

I think generated constraint names were generally "$1", "$2", etc. at

some point, instead of the more readable ones you get today.  But this

must be ancient.

Good point.  A bit of git-blame'ing shows that this documentation
wording appeared in e560dd353 of 2003-11-05, but we changed the
generation rule to not be "$n" in 45616f5bb of 2004-06-10.
(Oddly, I moved this documentation text around in 2005 without
noticing it was obsolete; or perhaps I did realize that but figured
it was still applicable to versions in the field.)

I concur with David that we should just drop the para.  It's merely
confusing now.  If you have a generated constraint name, it won't
require double-quoting unless your table or column name does, and
if they do you are doubtless already quite familiar with how
quoting works.

           regards, tom lane

Thank you all.

In order not to open a new thread, (small clarification)

On the tutorial-agg page in the code example

SELECT city FROM weather WHERE temp_lo = max(temp_lo); WRONG

you need to add a comment before WRONG