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From: Tom Lane <tgl@sss.pgh.pa.us>
To: "David G. Johnston" <david.g.johnston@gmail.com>
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Subject: Re: Generated names (suffix) for constraints not described in docs
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Comments: In-reply-to "David G. Johnston" <david.g.johnston@gmail.com>
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"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Wednesday, November 13, 2024, "Сергей П (SergeiDos)" <
> podrezov.sergey@gmail.com> wrote:
>> In the documentation for the Constraints section
>> https://www.postgresql.org/docs/current/ddl-constraints.html there is a
>> phrase: "So, to specify a named constraint, use the key word CONSTRAINT
>> followed by an identifier followed by the constraint definition. (If you
>> can't specify a constraint name in this way, the system choose a name for
>> you.)"
>> But nowhere in the documentation are the rules by which it generates names
>> on its own described.

> Correct.  Which means the specific name chosen is an implementation detail
> that can change at any time and should not be relied upon by the
> DBA.

Indeed.  I double-checked the SQL spec and found that it says

         3) If <constraint name definition> is not specified, then a
            <constraint name definition> that contains an implementation-
            dependent <constraint name> is implicit. The assigned
            <constraint name> shall obey the Syntax Rules of an explicit
            <constraint name>.

"Implementation-dependent" is standards-ese for "implementations
don't have to document their exact behavior".  (If it said
"implementation-defined", that would mean we should.)  So not
documenting it is expected.  I think we have indeed changed the
details around this in the past.

			regards, tom lane