Message-ID: <ffd7937d-190c-4f09-9418-5345728b45c4@iki.fi>
Date: Tue, 2 Jul 2024 15:59:45 +0300
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: Inline non-SQL SRFs using SupportRequestSimplify
To: Paul Jungwirth <pj@illuminatedcomputing.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
References: <09de6afa-c33d-4d94-a5cb-afc6cea0d2bb@illuminatedcomputing.com>
Content-Language: en-US
From: Heikki Linnakangas <hlinnaka@iki.fi>
In-Reply-To: <09de6afa-c33d-4d94-a5cb-afc6cea0d2bb@illuminatedcomputing.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Archived-At: <https://www.postgresql.org/message-id/ffd7937d-190c-4f09-9418-5345728b45c4%40iki.fi>
Precedence: bulk

On 28/06/2024 01:01, Paul Jungwirth wrote:
> If it seems good to let people use SupportRequestSimplify to make their SRFs be inlineable, I'm
> happy to add tests and docs. We should really document the idea of inlined functions in general, so
> I'll do that too.
>
> Another approach I considered is using a separate support request, e.g. SupportRequestInlineSRF, and
> just calling it from inline_set_returning_function. I didn't like having two support requests that
> did almost exactly the same thing. OTOH my current approach means you'll get an error if you do this:
> 
> ```
> postgres=# select temporal_semijoin('employees', 'id', 'valid_at', 'positions', 'employee_id',
> 'valid_at');
> ERROR:  unrecognized node type: 66
> ```
> 
> I'll look into ways to fix that.

If the support function returns a Query, we end up having a FuncExpr 
with a Query in the tree. A Query isnt an Expr, which is why you get 
that error, and it seems like a recipe for confusion in general. Perhaps 
returning a SubLink would be better.

I think we should actually add an assertion after the call to the 
SupportRequestSimplify support function, to check that it returned an 
Expr node.

+1 to the general feature of letting SRFs be simplified by the support 
function.

> I think SupportRequestSimplify is a really cool feature. It is nearly like having macros.
> I'm dreaming about other ways I can (ab)use it.

:-D

-- 
Heikki Linnakangas
Neon (https://neon.tech)