Horton

Re: SQL:2023 JSON simplified accessor support

Mark Dilger <mark.dilger@enterprisedb.com>

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From: Mark Dilger <mark.dilger@enterprisedb.com>
To: Alexandra Wang <alexandra.wang.oss@gmail.com>
Cc: Matheus Alcantara <matheusssilv97@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, Andrew Dunstan <andrew@dunslane.net>, Nikita Glukhov <glukhov.n.a@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, "David E. Wheeler" <david@justatheory.com>, jian he <jian.universality@gmail.com>
Date: 2025-03-04T14:05:18Z
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. Add test coverage for indirection transformation

  2. Fix typo in comment

  3. Implementation of subscripting for jsonb

On Mon, Mar 3, 2025 at 12:23 PM Alexandra Wang <alexandra.wang.oss@gmail.com>
wrote:

>  I've attached v10, which addresses your feedback.
>
>
Hi Alex!  Thanks for the patches.

In src/test/regress/sql/jsonb.sql, the section marked with "-- slices are
not supported" should be relabeled.  That comment predates these patches,
and is now misleading.

A bit further down in expected/jsonb.out, there is an expected failure, but
no SQL comment to indicate that it is expected:

+SELECT (t.jb).* FROM test_jsonb_dot_notation;
+ERROR:  missing FROM-clause entry for table "t"
+LINE 1: SELECT (t.jb).* FROM test_jsonb_dot_notation;

Perhaps a "-- fails" comment would clarify?  Then, further down,

+SELECT (jb).a.**.x FROM test_jsonb_dot_notation; -- not supported
+ERROR:  syntax error at or near "**"
+LINE 1: SELECT (jb).a.**.x FROM test_jsonb_dot_notation;

I wonder if it would be better to have the parser handle this case and
raise a ERRCODE_FEATURE_NOT_SUPPORTED instead?

I got curious about the support for this new dot notation in the plpgsql
parser and tried:

+DO $$
+DECLARE
+  a jsonb := '[1,2,3,4,5,6,7]'::jsonb;
+BEGIN
+  WHILE a IS NOT NULL
+  LOOP
+    RAISE NOTICE '%', a;
+    a := a[2:];
+  END LOOP;
+END
+$$ LANGUAGE plpgsql;
+NOTICE:  [1, 2, 3, 4, 5, 6, 7]
+NOTICE:  [3, 4, 5, 6, 7]
+NOTICE:  [5, 6, 7]
+NOTICE:  7

which looks good!  But then I tried:

+DO $$
+DECLARE
+  a jsonb := '{"": 6, "NU": [{"": [[3]]}, [6], [2], "bCi"], "aaf": [-6,
-8]}'::jsonb;
+BEGIN
+  WHILE a IS NOT NULL
+  LOOP
+    RAISE NOTICE '%', a;
+    a := COALESCE(a."NU", a[2]);
+  END LOOP;
+END
+$$ LANGUAGE plpgsql;
+NOTICE:  {"": 6, "NU": [{"": [[3]]}, [6], [2], "bCi"], "aaf": [-6, -8]}
+ERROR:  missing FROM-clause entry for table "a"
+LINE 1: a := COALESCE(a."NU", a[2])
+                      ^
+QUERY:  a := COALESCE(a."NU", a[2])
+CONTEXT:  PL/pgSQL function inline_code_block line 8 at assignment

which suggests the plpgsql parser does not recognize a."NU" as we'd
expect.  Any thoughts on this?

I notice there are no changes in src/interfaces/ecpg/test, which concerns
me.  The sqljson.pgc and sqljson_jsontable.pgc files are already testing
json handling in ecpg; perhaps just extend those a bit?

—
Mark Dilger
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