How to get RelationName ??

On Wednesday 10 March 2004 09:58 am, Ramanujam H S Iyengar wrote:

Hello,

How can i get the name of a relation from its Oid ?? I have seen some
functions in utils/cache/relcache.h like RelationIdGetRelation - which
gives Relation Node from Oid RelationSysNameGetRelation - which gives
Relation node for only the System names.

Can anyone please tell me how to get Relation node from relation name ???

Won't you have to go get the data from the database for this? I mean
actually execute the query:

select relname from pg_class where oid = 1234;

--
Jonathan Gardner
jgardner@jonathangardner.net

Hello,
Sorry for the previous confusing mail ..

iam in need of a function through which i can get a Relation Node given its
name ..
precisely the same one equivalent to " RelationSysNameGetRelation " .. which
works for all types of relations (system and user tables)

On Wednesday 10 March 2004 09:58 am, Ramanujam H S Iyengar wrote:

Hello,

How can i get the name of a relation from its Oid ?? I have seen some
functions in utils/cache/relcache.h like RelationIdGetRelation - which
gives Relation Node from Oid RelationSysNameGetRelation - which gives
Relation node for only the System names.

Can anyone please tell me how to get Relation node from relation name ???

Won't you have to go get the data from the database for this? I mean
actually execute the query:

Iam trying to test for some patch in the code of the Optimizer(planner) and
so I need some C functions, which does the job. I think we must have some
functions like the ones i have mentioned for the purpose. isin't it ??

regards,
-Ramu

select relname from pg_class where oid = 1234;

--
Jonathan Gardner
jgardner ( at ) jonathangardner ( dot ) net

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"Ramanujam H S Iyengar" <hals_ramu@hotmail.com> writes:

iam in need of a function through which i can get a Relation Node given its
name ..
precisely the same one equivalent to " RelationSysNameGetRelation " .. which
works for all types of relations (system and user tables)

The reason RelationSysNameGetRelation only works for system relations is
that it assumes the schema name is "pg_catalog". For non-system
relations you cannot do a lookup based only on relation name, because
there's no certainty that the result is unique.

There are some functions in catalog/namespace.c that can do lookup of an
unqualified name relative to the current schema search path, if that's
what you want.

Iam trying to test for some patch in the code of the Optimizer(planner) and
so I need some C functions, which does the job.

The optimizer has no need, ever, to find a relation by name; all it ever
sees are predigested relation OIDs. So you are not making a lot of
sense here. You certainly cannot assume that a search-path lookup is
appropriate for a relation that the optimizer is dealing with.

regards, tom lane

"Ramanujam H S Iyengar" <hals_ramu ( at ) hotmail ( dot ) com> writes:
iam in need of a function through which i can get a Relation Node given
its name ..
precisely the same one equivalent to " RelationSysNameGetRelation " ..
which works for all types of relations (system and user tables)

The reason RelationSysNameGetRelation only works for system relations is
that it assumes the schema name is "pg_catalog". For non-system
relations you cannot do a lookup based only on relation name, because
there's no certainty that the result is unique.

There are some functions in catalog/namespace.c that can do lookup of an
unqualified name relative to the current schema search path, if that's
what you want.

Thanks a lot,
The function RelnameGetRelid(const char *) is working for me !!

Iam trying to test for some patch in the code of the Optimizer(planner)
and so I need some C functions, which does the job.

The optimizer has no need, ever, to find a relation by name; all it ever
sees are predigested relation OIDs. So you are not making a lot of
sense here. You certainly cannot assume that a search-path lookup is
appropriate for a relation that the optimizer is dealing with.

regards, tom lane

Iam trying to put in some other module of optimizer that we have developed,
which works on relation name and gives the optimal plan. Iam trying to
convert the plans given by this(our) optimizer to the
Plan structure of PostgreSQL. So finally i have to convert the Relation
names back to their relOids.

All this in the process of using the execution engine of Postgres for our
optimizer module !! :-)

Thats why i was asking !!

Thanks

-Ramu

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"Ramanujam H S Iyengar" <hals_ramu@hotmail.com> writes:

The optimizer has no need, ever, to find a relation by name; all it ever
sees are predigested relation OIDs. So you are not making a lot of
sense here. You certainly cannot assume that a search-path lookup is
appropriate for a relation that the optimizer is dealing with.

Iam trying to put in some other module of optimizer that we have developed,
which works on relation name and gives the optimal plan. Iam trying to
convert the plans given by this(our) optimizer to the
Plan structure of PostgreSQL. So finally i have to convert the Relation
names back to their relOids.

If your optimizer emits unqualified relation names then it is broken,
as it will never be safe to use in the presence of schemas. People
will not want to use a database that might apply updates meant for
"a.foo" to "b.foo".

regards, tom lane