Horton

Re: remaining sql/json patches

Robert Haas <robertmhaas@gmail.com>

View thread
From: Robert Haas <robertmhaas@gmail.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Amit Langote <amitlangote09@gmail.com>, jian he <jian.universality@gmail.com>, Andres Freund <andres@anarazel.de>, Andrew Dunstan <andrew@dunslane.net>, Erik Rijkers <er@xs4all.nl>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2023-12-07T17:19:24Z
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.

On Wed, Dec 6, 2023 at 10:26 AM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> > I think I'm inclined toward adapting the LA-token fix (attached 0005),
> > because we've done that before with SQL/JSON constructors patch.
> > Also, if I understand the concerns that Tom mentioned at [1]
> > correctly, maybe we'd be better off not assigning precedence to
> > symbols as much as possible, so there's that too against the approach
> > #1.
>
> Sounds ok to me, but I'm happy for this decision to be overridden by
> others with more experience in parser code.

In my experience, the lookahead solution is typically suitable when
the keywords involved aren't used very much in other parts of the
grammar. I think the situation that basically gets you into trouble is
if there's some way to have a situation where NESTED shouldn't be
changed to NESTED_LA when PATH immediately follows. For example, if
NESTED could be used like DISTINCT in a SELECT query:

SELECT DISTINCT a, b, c FROM whatever

...then that would be a strong indication in my mind that we shouldn't
use the lookahead solution, because what if you substitute "path" for
"a"? Now you have a mess.

I haven't gone over the grammar changes in a lot of detail so I'm not
sure how much risk there is here. It looks to me like there's some
syntax that goes NESTED [PATH] 'literal string', and if that were the
only use of NESTED or PATH then I think we'd be completely fine. I see
that PATH b_expr also gets added to xmltable_column_option_el, and
that's a little more worrying, because you don't really want to see
keywords that are used for special lookahead rules in places where
they can creep into general expressions, but it seems like it might
still be OK as long as NESTED doesn't also start to get used in other
places. If you ever create a situation where NESTED can bump up
against PATH without wanting that to turn into NESTED_LA PATH, then I
think it's likely that this whole approach will unravel. As long as we
don't think that will ever happen, I think it's probably OK. If we do
think it's going to happen, then we should probably grit our teeth and
use precedence.

-- 
Robert Haas
EDB: http://www.enterprisedb.com