Re: remaining sql/json patches

On Mon, Jul 10, 2023 at 11:52 PM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> I forgot to add:

Thanks for the review of these.

> * 0001 looks an obvious improvement. You could just push it now, to
> avoid carrying it forward anymore. I would just put the constructName
> ahead of value expr in the argument list, though.

Sure, that makes sense.

> * 0002: I have no idea what this is (though I probably should). I would
> also push it right away -- if anything, so that we figure out sooner
> that it was actually needed in the first place. Or maybe you just need
> the right test cases?

Hmm, I don't think having or not having CaseTestExpr makes a
difference to the result of evaluating JsonValueExpr.format_expr, so
there are no test cases to prove one way or the other.

After staring at this again for a while, I think I figured out why the
CaseTestExpr might have been put there in the first place. It seems
to have to do with the fact that JsonValueExpr.raw_expr is currently
evaluated independently of JsonValueExpr.formatted_expr and the
CaseTestExpr propagates the result of the former to the evaluation of
the latter. Actually, formatted_expr is effectively
formatting_function(<result-of-raw_expr>), so if we put raw_expr
itself into formatted_expr such that it is evaluated as part of
evaluating formatted_expr, then there is no need for the CaseTestExpr
as the propagator for raw_expr's result.

I've expanded the commit message to mention the details.

I'll push these tomorrow.

On Mon, Jul 10, 2023 at 11:47 PM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> On 2023-Jul-10, Amit Langote wrote:
> > > I'm not in love with the fact that JSON and JSONB have pretty much
> > > parallel type categorizing functionality. It seems entirely artificial.
> > > Maybe this didn't matter when these were contained inside each .c file
> > > and nobody else had to deal with that, but I think it's not good to make
> > > this an exported concept. Is it possible to do away with that? I mean,
> > > reduce both to a single categorization enum, and a single categorization
> > > API. Here you have to cast the enum value to int in order to make
> > > ExecInitExprRec work, and that seems a bit lame; moreso when the
> > > "is_jsonb" is determined separately (cf. ExecEvalJsonConstructor)
> >
> > OK, I agree that a unified categorizing API might be better. I'll
> > look at making this better. Btw, does src/include/common/jsonapi.h
> > look like an appropriate place for that?
>
> Hmm, that header is frontend-available, and the type-category appears to
> be backend-only, so maybe no. Perhaps jsonfuncs.h is more apropos?
> execExpr.c is already dealing with array internals, so having to deal
> with json internals doesn't seem completely out of place.

OK, attached 0003 does it like that. Essentially, I decided to only
keep JsonTypeCategory and json_categorize_type(), with some
modifications to accommodate the callers in jsonb.c.

> > > In the 2023 standard, JSON_SCALAR is just
> > >
> > > <JSON scalar> ::= JSON_SCALAR <left paren> <value expression> <right paren>
> > >
> > > but we seem to have added a <JSON output format> clause to it. Should
> > > we really?
> >
> > Hmm, I am not seeing <JSON output format> in the rule for JSON_SCALAR,
>
> Agh, yeah, I confused myself, sorry.
>
> > Per what I wrote above, the grammar for JSON() and JSON_SCALAR() does
> > not allow specifying the FORMAT clause. Though considering what you
> > wrote, the RETURNING clause does appear to be an extension to the
> > standard's spec.
>
> Hmm, I see that <JSON output clause> (which is RETURNING plus optional
> FORMAT) appears included in JSON_OBJECT, JSON_ARRAY, JSON_QUERY,
> JSON_SERIALIZE, JSON_OBJECTAGG, JSON_ARRAYAGG. It's not necessarily a
> bad thing to have it in other places, but we should consider it
> carefully. Do we really want/need it in JSON() and JSON_SCALAR()?

I thought that removing that support breaks JSON_TABLE() or something
but it doesn't, so maybe we can do without the extension if there's no
particular reason it's there in the first place. Maybe Andrew (cc'd)
remembers why he decided in [1] to (re-) add the RETURNING clause to
JSON() and JSON_SCALAR()?

Updated patches, with 0003 being a new refactoring patch, are
attached. Patches 0004~ contain a few updates around JsonValueExpr.
Specifically, I removed the case for T_JsonValueExpr in
transformExprRecurse(), because I realized that JsonValueExpr
expressions never appear embedded in other expressions. That allowed
me to get rid of some needless refactoring around
transformJsonValueExpr() in the patch that adds JSON_VALUE() etc.

--
Thanks, Amit Langote
EDB: http://www.enterprisedb.com

[1] https://www.postgresql.org/message-id/1d44d832-4ea9-1ec9-81e9-bc6b2bd8cc43%40dunslane.net