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Re: find column OID types with information schema?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Whit Armstrong <armstrong(dot)whit(at)gmail(dot)com>
Cc: pgsql-general <pgsql-general(at)postgresql(dot)org>
Subject: Re: find column OID types with information schema?
Date: 2009-04-27 17:09:46
Message-ID: 7188.1240852186@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-general
Whit Armstrong <armstrong(dot)whit(at)gmail(dot)com> writes:
> Am I misinterpreting this documentation?  Are there cases in which the
> OID's of two tables will collide?  I don't see any uniqueness
> constraints on the pg_class table.

You didn't look too hard:

regression=# \d pg_class
...
Indexes:
    "pg_class_oid_index" UNIQUE, btree (oid)
    "pg_class_relname_nsp_index" UNIQUE, btree (relname, relnamespace)

All system catalogs that have OIDs at all effectively treat them as a
primary key.  If they weren't unique identifiers they wouldn't be good
for much ...

What the documentation is trying to point out is that the uniqueness
guarantees don't extend across tables.  So for example a table and a
datatype could by coincidence have the same OID, since they live in
different system catalogs.

			regards, tom lane

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