interperting type oid in C code

SELECT typname
FROM pg_type
WHERE oid = Oid_x;

On Mon, Oct 19, 2015 at 2:36 PM, Ken Been <kbbeen@gmail.com> wrote:

I'm working on a foreign data wrapper and I want to switch based on the
column type. Specifically, if the column type in the external table is the
same as in the (locally defined) foreign table then I can get some speedup
for some types.

Through the ForeignScanState object I can get TupleDesc and AttInMetadata
opjects, and through there I can get the Oid of the column type, but now
I'm stumped. How can I programmatically check whether Oid X refers to type
int4, or whatever?

Thanks.

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*Melvin Davidson*
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Thanks, but I actually wanted to do it from C code. But anyway I think I
found the answer: use the symbolic constants in catalog/pg_type.h, such as
INT4OID.

On Mon, Oct 19, 2015 at 6:44 PM, Melvin Davidson <melvin6925@gmail.com>
wrote:

Ken Been wrote:

Thanks, but I actually wanted to do it from C code. But anyway I think I
found the answer: use the symbolic constants in catalog/pg_type.h, such as
INT4OID.

You can probably use
SearchSysCache1(TYPEOID, ObjectIdGetDatum(your_oid))
or perhaps
lookup_type_cache(your_oid).

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�lvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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Those are more complicated, and it's not obvious to me how to use them. I
really think that all I need is something as simple as "if (my_oid ==
INT4OID) {...}". Is there any reason why I shouldn't just do that?

On Mon, Oct 19, 2015 at 7:08 PM, Alvaro Herrera <alvherre@2ndquadrant.com>
wrote:

Ken Been wrote:

Those are more complicated, and it's not obvious to me how to use them. I
really think that all I need is something as simple as "if (my_oid ==
INT4OID) {...}". Is there any reason why I shouldn't just do that?

I don't know. I was thinking that you might want to handle a larger set
of type OIDs.

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PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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Well, it's a few types, but the logic is different for each one, so they
have to be handled independently anyway.

On Mon, Oct 19, 2015 at 7:40 PM, Alvaro Herrera <alvherre@2ndquadrant.com>
wrote:

Ken Been wrote:

I'm working on a foreign data wrapper and I want to switch based on the column type.
Specifically, if the column type in the external table is the same as in the (locally defined) foreign
table then I can get some speedup for some types.

Through the ForeignScanState object I can get TupleDesc and AttInMetadata opjects, and
through there I can get the Oid of the column type, but now I'm stumped. How can I programmatically
check whether Oid X refers to type int4, or whatever?

Thanks, but I actually wanted to do it from C code. But anyway I think I found the answer: use the
symbolic constants in catalog/pg_type.h, such as INT4OID.

That's fine, there is no problem with doing that.

Yours,
Laurenz Albe

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