Horton

Re: remaining sql/json patches

amit <amitlangote09@gmail.com>

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From: Amit Langote <amitlangote09@gmail.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2023-07-10T12:56:27Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. SQL/JSON: Various improvements to SQL/JSON query function docs

  2. SQL/JSON: Fix some obsolete comments.

  3. SQL/JSON: Fix issues with DEFAULT .. ON ERROR / EMPTY

  4. JSON_TABLE: Add support for NESTED paths and columns

  5. Fix JsonExpr deparsing to emit QUOTES and WRAPPER correctly

  6. Fix typo introduced in 6185c9737

  7. Add basic JSON_TABLE() functionality

  8. Avoid splitting errmsg string to span multiple lines

  9. Add SQL/JSON query functions

  10. Implement various jsonpath methods

  11. Add soft error handling to some expression nodes

  12. Adjust populate_record_field() to handle errors softly

  13. Refactor code used by jsonpath executor to fetch variables

  14. Test EXPLAIN (FORMAT JSON) ... XMLTABLE

  15. Simplify productions for FORMAT JSON [ ENCODING name ]

  16. Add trailing commas to enum definitions

  17. doc: add missing <returnvalue> and whitespace

  18. Add more SQL/JSON constructor functions

  19. Rename a nonterminal used in SQL/JSON grammar

  20. Some refactoring to export json(b) conversion functions

  21. Don't include CaseTestExpr in JsonValueExpr.formatted_expr

  22. Code review for commit b6e1157e7d

  23. Pass constructName to transformJsonValueExpr()

  24. Unify JSON categorize type API and export for external use

  25. Make some indentation in gram.y consistent

  26. Allow most keywords to be used as column labels without requiring AS.

  27. Reduce size of backend scanner's tables.

  28. Use perfect hashing, instead of binary search, for keyword lookup.

Attachments

Hi Alvaro,

On Fri, Jul 7, 2023 at 9:28 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> Looking at 0001 now.

Thanks.

> I noticed that it adds JSON, JSON_SCALAR and JSON_SERIALIZE as reserved
> keywords to doc/src/sgml/keywords/sql2016-02-reserved.txt; but those
> keywords do not appear in the 2016 standard as reserved.  I see that
> those keywords appear as reserved in sql2023-02-reserved.txt, so I
> suppose you're covered as far as that goes; you don't need to patch
> sql2016, and indeed that's the wrong thing to do.

Yeah, fixed that after Peter pointed it out.

> I see that you add json_returning_clause_opt, but we already have
> json_output_clause_opt.  Shouldn't these two be one and the same?
> I think the new name is more sensible than the old one, since the
> governing keyword is RETURNING; I suppose naming it "output" comes from
> the fact that the standard calls this <JSON output clause>.

One difference between the two is that json_output_clause_opt allows
specifying the FORMAT clause in addition to the RETURNING type name,
while json_returning_clause_op only allows specifying the type name.

I'm inclined to keep only json_returning_clause_opt as you suggest and
make parse_expr.c output an error if the FORMAT clause is specified in
JSON() and JSON_SCALAR(), so turning the current syntax error on
specifying RETURNING ... FORMAT for these functions into a parsing
error.   Done that way in the attached updated patch and also updated
the latter patch that adds JSON_EXISTS() and JSON_VALUE() to have
similar behavior.

> typo "requeted"

Fixed.

> 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?

> 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,
which looks like this in the current grammar:

func_expr_common_subexpr:
...
            | JSON_SCALAR '(' a_expr json_returning_clause_opt ')'
                {
                    JsonScalarExpr *n = makeNode(JsonScalarExpr);

                    n->expr = (Expr *) $3;
                    n->output = (JsonOutput *) $4;
                    n->location = @1;
                    $$ = (Node *) n;
                }
...
json_returning_clause_opt:
            RETURNING Typename
                {
                    JsonOutput *n = makeNode(JsonOutput);

                    n->typeName = $2;
                    n->returning = makeNode(JsonReturning);
                    n->returning->format =
                        makeJsonFormat(JS_FORMAT_DEFAULT, JS_ENC_DEFAULT, @2);
                    $$ = (Node *) n;
                }
            | /* EMPTY */                           { $$ = NULL; }
            ;

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.  I can't find any reasoning in the original
discussion as to how that came about, except an email from Andrew [1]
saying that he added it back to the patch.

Here's v3 in the meantime.

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

[1] https://www.postgresql.org/message-id/flat/cd0bb935-0158-78a7-08b5-904886deac4b%40postgrespro.ru