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From: jian he <jian.universality@gmail.com>
Date: Thu, 17 Aug 2023 00:32:08 +0800
Message-ID: <CACJufxH7ftu9HD+h_gDWPDvq1ZO8vGm81JomSKjvQacCLMLcxg@mail.gmail.com>
Subject: Re: Extract numeric filed in JSONB more effectively
To: Andy Fan <zhihui.fan1213@gmail.com>
Cc: Pavel Stehule <pavel.stehule@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, 
	Chapman Flack <chap@anastigmatix.net>, pgsql-hackers <pgsql-hackers@postgresql.org>
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On Wed, Aug 16, 2023 at 2:28=E2=80=AFPM Andy Fan <zhihui.fan1213@gmail.com>=
 wrote:
>
> update with the correct patch..

regression=3D# select proname, pg_catalog.pg_get_function_arguments(oid)
from pg_proc
where proname =3D  'jsonb_extract_path_type';
         proname         |                     pg_get_function_arguments
-------------------------+-------------------------------------------------=
-------------------
 jsonb_extract_path_type | from_json jsonb, VARIADIC path_elems
text[], target_oid anyelement
(1 row)

VARIADIC should be the last argument?

select jsonb_array_element_type(jsonb'[1231]',0, null::int);
now return null.
Should it return 1231?

regression=3D# select jsonb_array_element_type(jsonb'1231',0, 1::int);
 jsonb_array_element_type
--------------------------
                     1231
(1 row)

not sure if it's ok. if you think it's not ok then:
+ if (!JB_ROOT_IS_ARRAY(jb))
+PG_RETURN_NULL();
change to
+if (JB_ROOT_IS_SCALAR(jb) || !JB_ROOT_IS_ARRAY(jb))
+PG_RETURN_NULL();

select jsonb_array_element_type(jsonb'[1231]',0, '1'::jsonb);
will crash, because jsonb_array_element_type call
cast_jsonbvalue_to_type then in switch case, it will go to
default part. in default part you have Assert(false);
also in cast_jsonbvalue_to_type, PG_RETURN_POINTER(NULL) code won't be reac=
hed.

in jsonb_cast_support function. you already have
!jsonb_cast_is_optimized(fexpr->funcresulttype)). then in the default
branch of cast_jsonbvalue_to_type, you can just elog(error, "can only
cast to xxx type"). jsonb_array_element_type, jsonb_object_field_type,
 third argument is anyelement. so targetOid can be any datatype's oid.