Re: RowDescription for a function does not include table OID

Maxwell Dreytser <Maxwell(dot)Dreytser(at)assistek(dot)com> writes:
> I am working on a meta-programming use-case where I need to scrape some detailed information about the results of a function that "RETURNS TABLE (LIKE physical_table)", which ends up with prorettype = 'physical_table'::regtype.
> The problem is that for the query "SELECT * FROM my_function()" the RowDescription that is sent back shows 0 for Table OID and Column Index.

Yes, that's expected. You're selecting from a function, not a table.

> I would expect that the Table OID contains the relation OID of this
> table, as it would do for a typical statement like "SELECT * FROM
> my_table".

The PG wire protocol specification [1] defines these fields thus:

If the field can be identified as a column of a specific
table, the object ID of the table; otherwise zero.

If the field can be identified as a column of a specific
table, the attribute number of the column; otherwise zero.

My reading of that is that we should populate these fields only for
the case of direct selection from a table. If you go further than
that, then first off you have a ton of definitional issues (should it
"look through" views, for example?), and second you probably break
applications that are expecting the existing, longstanding definition.

regards, tom lane

[1] https://www.postgresql.org/docs/current/protocol-message-formats.html