Re: Proposal to CREATE FOREIGN TABLE LIKE - Mailing list pgsql-hackers

On Mon, Feb 17, 2025 at 07:14:59PM +0800, Zhang Mingli wrote:

On Feb 17, 2025 at 15:24 +0800, Michael Paquier <michael@paquier.xyz>, wrote:

+ * For foreign tables, they have no storage in Postgres.
+ * Inapplicable options are ignored.

Wording is a bit strange here.

 * Foreign tables do not store data in Postgres.
 * Any options that are not applicable for foreign tables will be ignored:

I would do something like that, perhaps, though I could get that
people don't like this suggestion:
"Some options are ignored. For example, as foreign tables have no
storage, these options have no effect: storage, compression, identity
and indexes. Similarly, INCLUDING INDEXES is ignored from a view."

I also didn't realize this until I wrote this patch. This could be
useful for the planner？

Constraints can be used as hints in the planner when working on
foreign tables. I'm pretty sure that this is the same reason here,
seeing that this is supported since v10 where statistics have been
introduced. I would need to dig more into the code, but that's not
really the point for this thread..

+ Inapplicable options: <literal>INCLUDING INDEXES</literal>, <literal>INCLUDING STORAGE</literal>,
+ <literal>INCLUDING COMPRESSION</literal>, <literal>INCLUDING IDENTITY</literal> are ignored.

I would remove this paragraph, actually. The options supported are
listed by your patch, and that would be one area less to update if a
new INCLUDING flavor is added.

Copy-pasting the details of how the LIKE options work to the
create_foreign_table.sgml page is OK for me, and perhaps this will
diverge a bit from the CREATE TABLE part. One thing is that LIKE is
not part of the SQL specification for CREATE FOREIGN TABLE. Perhaps
this should be mentioned at the bottom of the page under the
"compatibility" section?