Re: Support for CREATE MODULE?

On Thu, Jun 3, 2021 at 8:49 AM Peter Eisentraut
<peter(dot)eisentraut(at)enterprisedb(dot)com> wrote:
> Given that, as you said, the concept of modules is in the SQL standard,
> there is surely some guidance in there about how this is supposed to
> affect name resolution. So let's start with that. Maybe we won't like
> it in the end or whatever, but we should surely look there first.

Studying the spec further, catalog/schema/module are all used to
identify a module-level routine. I don't see it spelled out that
is needs to be in that format of catalog.schema.module.routine to
fully qualify the routine, but it would likely be awkward for users
to come up with an alternative syntax like
(catalog.schema.module).routine or catalog.scheme.module->routine

The way the spec is worded, I read it as that schemas take precedence
over modules regarding path resolution. So for example with 2-level
naming if there is a schema 'foo' and a module 'public.foo' both with
functions 'bar' 'foo.bar' would refer to the schema-level function not
the module-level function. I've not found guidance on throwing catalog
into the mix and 3-level naming. Say we had a catalog 'postgres' with a
schema 'foo' with a function 'bar' and a schema 'postgres' with a module
'foo' with a function 'bar'. What would 'postgres.foo.bar' refer to? If
the SQL was executed from a catalog other than 'postgres', we'd have no
way of knowing if 'foo.bar' existed there. So if it's implementation
dependent, saying schemas take precedence over catalogs may make sense
and 'postgres.foo.bar' refers to the module-level function in the
'postgres' schema.