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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: 2025-03-04T15:34:53Z
Lists: pgsql-hackers

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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 Tue, Mar 4, 2025 at 6:05 AM Mark Dilger <mark.dilger@enterprisedb.com>
wrote:

> 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 should mention that

+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]}
+NOTICE:  [{"": [[3]]}, [6], [2], "bCi"]
+NOTICE:  [2]

works fine.  I guess that is good enough.  Should we add these to the
sql/jsonb.sql to document the expected behavior, both with the error when
using plain "a" and with the correct output when using "(a)"?  The reason I
mention this is that the plpgsql parser might get changed at some point,
and without a test case, we might not notice if this breaks.

—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company