Kevin Brown wrote:
> Tom Lane wrote:
> > "Andrew Dunstan" <andrew@dunslane.net> writes:
> > >> I object to creating gratuitous incompatibilities with the SQL standard,
> > >> which will obstruct legitimate features down the road.  The SQL standard
> > >> says it is <schema>.<constraint>.
> > 
> > > Is there a case for enforcing uniqueness on constraint names, then?
> > 
> > Other than "SQL92 says so"?  Very little.  This seems to me to be a
> > design error in the spec.  Per-table constraint names are easier to
> > work with --- if they're global across a schema then you have a serious
> > problem avoiding collisions.
> 
> I assume that SQL99 and later don't specify anything different than what
> SQL92 calls for in this regard?
> 
> Without any meaningful guidance from the spec, the best we can do is
> support per-table constraint names and provide optional (via a GUC
> variable) support for SQL92-compliant constraint names.  Let the DBA
> decide which (if not both) is best for his situation.  Inasmuch as
> one of our "selling points" is our compliance with the SQL spec, I see
> little reason to entirely avoid compliance with the spec on this issue --
> just make it possible to do something else when/if necessary.
> 
> The two approaches aren't necessarily mutually exclusive (though SQL99
> compliance on constraint names would obviously make it unnecessary to
> specify a tablename along with a constraint name), so I see little
> problem here.  But the current arrangement is obviously untenable,
> because it allows you to create a situation (multiple constraints by
> the same name) that you can't reasonably extricate yourself from.

Well, it seems if we want to continue to allow the same constraint name
to be used by different tables in the same schema, we have to print the
tablename in the error message.  Would someone actually be looking for a
standards-compliant error string?  We have already extended the standard
--- either we revert that, or we have to go the entire way and print the
table name.

-- 
  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

Mon, 25 Aug 2003 23:57:49 -0400 (EDT)
Bruce Momjian <pgman@candle.pha.pa.us>
Re: set constraints docs page
Bruce Momjian wrote:
> Kevin Brown wrote:
> > The two approaches aren't necessarily mutually exclusive (though SQL99
> > compliance on constraint names would obviously make it unnecessary to
> > specify a tablename along with a constraint name), so I see little
> > problem here.  But the current arrangement is obviously untenable,
> > because it allows you to create a situation (multiple constraints by
> > the same name) that you can't reasonably extricate yourself from.
> 
> Well, it seems if we want to continue to allow the same constraint name
> to be used by different tables in the same schema, we have to print the
> tablename in the error message.  Would someone actually be looking for a
> standards-compliant error string?  We have already extended the standard
> --- either we revert that, or we have to go the entire way and print the
> table name.

If PG were configurable in terms of how it manages constraint names,
then it would depend on how the DBA had the database configured.  With it
configured to disallow name collisions, it would obviously be unnecessary
to report the table name, though I still think it would be useful (if
only because it gives a little extra context to work with).  But if it's
configured to allow name collisions, then it doesn't make sense not to
print the table name in an error message, because that's the only way to
guarantee that the DBA can identify which constraint is being referred to.


The problem as things stand now is that even if we printed the table name
involved, the DBA is placed in a difficult position if the constraint in
question isn't uniquely named -- which is the only case where printing
the table name would really matter.  That's because he can't actually
refer to the constraint in any unique way short of playing with the
system tables; he'd have to rename the constraint first before being
able to really do something with it (is this even possible for him to
do without manipulating system tables?  Is there an ALTER CONSTRAINT?).


-- 
Kevin Brown					      kevin@sysexperts.com

Wed, 27 Aug 2003 01:22:09 -0700
Kevin Brown <kevin@sysexperts.com>
Re: set constraints docs page
Kevin Brown wrote:
> Bruce Momjian wrote:
> > Kevin Brown wrote:
> > > The two approaches aren't necessarily mutually exclusive (though SQL99
> > > compliance on constraint names would obviously make it unnecessary to
> > > specify a tablename along with a constraint name), so I see little
> > > problem here.  But the current arrangement is obviously untenable,
> > > because it allows you to create a situation (multiple constraints by
> > > the same name) that you can't reasonably extricate yourself from.
> > 
> > Well, it seems if we want to continue to allow the same constraint name
> > to be used by different tables in the same schema, we have to print the
> > tablename in the error message.  Would someone actually be looking for a
> > standards-compliant error string?  We have already extended the standard
> > --- either we revert that, or we have to go the entire way and print the
> > table name.
> 
> If PG were configurable in terms of how it manages constraint names,
> then it would depend on how the DBA had the database configured.  With it
> configured to disallow name collisions, it would obviously be unnecessary
> to report the table name, though I still think it would be useful (if
> only because it gives a little extra context to work with).  But if it's
> configured to allow name collisions, then it doesn't make sense not to
> print the table name in an error message, because that's the only way to
> guarantee that the DBA can identify which constraint is being referred to.
> 
> 
> The problem as things stand now is that even if we printed the table name
> involved, the DBA is placed in a difficult position if the constraint in
> question isn't uniquely named -- which is the only case where printing
> the table name would really matter.  That's because he can't actually
> refer to the constraint in any unique way short of playing with the
> system tables; he'd have to rename the constraint first before being
> able to really do something with it (is this even possible for him to
> do without manipulating system tables?  Is there an ALTER CONSTRAINT?).

Added to TODO:

	* Print table names with constraint names in error messages, or make
	  constraint names unique within a schema

-- 
  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

Thu, 4 Sep 2003 20:50:19 -0400 (EDT)
Bruce Momjian <pgman@candle.pha.pa.us>
Re: set constraints docs page
Bruce Momjian wrote:
 
> Added to TODO:
> 
> 	* Print table names with constraint names in error messages, or make
> 	  constraint names unique within a schema


Should the TODO also include adding "ALTER TABLE x ALTER CONSTRAINT
y RENAME TO z" functionality if we don't make constraint names unique
within a schema?


-- 
Kevin Brown					      kevin@sysexperts.com

Thu, 4 Sep 2003 17:55:46 -0700
Kevin Brown <kevin@sysexperts.com>
Re: set constraints docs page
Kevin Brown wrote:
> Bruce Momjian wrote:
>  
> > Added to TODO:
> > 
> > 	* Print table names with constraint names in error messages, or make
> > 	  constraint names unique within a schema
> 
> 
> Should the TODO also include adding "ALTER TABLE x ALTER CONSTRAINT
> y RENAME TO z" functionality if we don't make constraint names unique
> within a schema?

Added to TODO:

	o Allow ALTER TABLE ... ALTER CONSTRAINT ... RENAME

-- 
  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

Thu, 4 Sep 2003 21:10:38 -0400 (EDT)
Bruce Momjian <pgman@candle.pha.pa.us>
Re: set constraints docs page