Обсуждение: The Information Schema vs the PG Catalog

I would say that pg_catalog is the more complete one whereas the
information_schema the more generic, standards-conformant place. I would
stick with the information_schema unless that becomes inadequate. A case
in point may be sequences. Apart from
information_schema.columns.column_default I haven't seen them
represented anywhere there (please someone correct me if I am wrong).
You can get more information about sequences from pg_catalog.pg_class
(look for pg_class.relkind='S') and various views that sit on top of
that (e.g. pg_statio_all_sequences).

George


> I'm writing PL/pgSQL routines that generate triggers, functions,
> and rules based on design characteristics of tables, columns, and
> other database objects.  These routines need to be able to look up
> the definitions of these objects.  I see that there are two places
> available to look up this info: the Information Schema and in the
> PG Catalog.
>
> Which source is preferable?  Or if that answer isn't absolute,
> what are the reasons or conditions for preferring one over the
> other?
>
> Also, a specific question:  Does the Information Schema offer any
> way to list the sequences that exist and their attributes?  I
> can't seem to find any.
>

Thanks, George.  What you say fits with what I was finding.  I think that's
the way I will go.

~ Ken

> -----Original Message-----
> From: George Pavlov [mailto:gpavlov@mynewplace.com]
> Sent: Tuesday, December 27, 2005 12:11 PM
> To: pgsql-sql@postgresql.org
> Cc: ken@sunward.org
> Subject: Re: The Information Schema vs the PG Catalog
> 
> I would say that pg_catalog is the more complete one whereas the
> information_schema the more generic, standards-conformant place. I would
> stick with the information_schema unless that becomes inadequate. A case
> in point may be sequences. Apart from
> information_schema.columns.column_default I haven't seen them
> represented anywhere there (please someone correct me if I am wrong).
> You can get more information about sequences from pg_catalog.pg_class
> (look for pg_class.relkind='S') and various views that sit on top of
> that (e.g. pg_statio_all_sequences).
> 
> George
> 
> 
> > I'm writing PL/pgSQL routines that generate triggers, functions,
> > and rules based on design characteristics of tables, columns, and
> > other database objects.  These routines need to be able to look up
> > the definitions of these objects.  I see that there are two places
> > available to look up this info: the Information Schema and in the
> > PG Catalog.
> >
> > Which source is preferable?  Or if that answer isn't absolute,
> > what are the reasons or conditions for preferring one over the
> > other?
> >
> > Also, a specific question:  Does the Information Schema offer any
> > way to list the sequences that exist and their attributes?  I
> > can't seem to find any.
> >