MIME-Version: 1.0
Date: Fri, 18 Aug 2023 15:08:57 -0400
From: Chapman Flack <chap@anastigmatix.net>
To: Andy Fan <zhihui.fan1213@gmail.com>
Cc: jian he <jian.universality@gmail.com>, Pavel Stehule
 <pavel.stehule@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers
 <pgsql-hackers@postgresql.org>
Subject: Re: Extract numeric filed in JSONB more effectively
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On 2023-08-18 14:50, Chapman Flack wrote:
> Now, my guess is EXPLAIN is complaining when it sees the Const
> of type internal, and doesn't know how to show that value.
> Perhaps makeRelabelType is the answer there, too: what if the
> Const has Oid type, so EXPLAIN can show it, and what's inserted
> as the function argument is a relabel node saying it's internal?

Simply changing the Const to be of type Oid makes EXPLAIN happy,
and nothing ever says "hey, why are you passing this oid for an
arg that wants internal?". This is without adding any relabel
nodes anywhere.

  Seq Scan on pg_temp.test_jsonb
    Output: pg_catalog.jsonb_array_element_type('23'::oid, test_json, 0), 
(test_json -> 0)
    Filter: (test_jsonb.json_type = 'scalarint'::text)

Nothing in that EXPLAIN output to make you think anything weird
was going on, unless you went and looked up jsonb_array_element_type
and saw that its arg0 isn't oid and its return type isn't int4.

But I don't know that adding relabel nodes wouldn't still be
the civilized thing to do.

Regards,
-Chap