Re: find column OID types with information schema?

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От Whit Armstrong
Тема Re: find column OID types with information schema?
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Msg-id 8ec76080904270945s1fda4273m315237ec54d58d2b@mail.gmail.com
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Ответ на Re: find column OID types with information schema?  (Tom Lane <tgl@sss.pgh.pa.us>)
Ответы Re: find column OID types with information schema?  (Tom Lane <tgl@sss.pgh.pa.us>)
Список pgsql-general
Thanks, Tom.

I guess the answer is, yes, but perhaps you can help me decide.

I'm just reading this part of the documentation from the link I
posted: "OIDs are not added to user-created tables, unless WITH OIDS
is specified when the table is created."  and also:

The oid type is currently implemented as an unsigned four-byte
integer. Therefore, it is not large enough to provide database-wide
uniqueness in large databases, or even in large individual tables. So,
using a user-created table's OID column as a primary key is
discouraged. OIDs are best used only for references to system tables.

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.  Or are there cases in which a
table does not have an OID in the pg_class table?   I apologize for
the dumb questions, but I'm just a little confused about the
internals.

Thanks,
Whit


On Mon, Apr 27, 2009 at 12:29 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Whit Armstrong <armstrong.whit@gmail.com> writes:
>> However, there is no example that uses a schema + tablename.
>
> If you're into masochism you can do that with a join of pg_class and
> pg_namespace.  But what's usually easier for one-off queries is to
> use the regclass converter:
>
> select attname, atttypid from pg_attribute
> where attrelid = 'myschema.mytable'::regclass;
>
> Most likely you'll also want
>
> ... and attnum > 0 and not attisdropped
>
> to keep down the clutter.
>
>                        regards, tom lane
>

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