Re: SQL:2023 JSON simplified accessor support

Hi Chao,

Thanks for reviewing. I'm glad you like the new approach of
introducing "transform_partial". I've attached v22, which addresses
some of your feedback, and I ran pgindent again.

See detailed replies below.

On Mon, Sep 22, 2025 at 10:48 PM Chao Li <li.evan.chao@gmail.com> wrote:

> The new approach of introducing “transform_partial” looks like a better
> solution, which leads to less code change to hstore_subs and arraysubs.
> However, when I tested the v21, I encountered errors when combine composite
> type, array and jsonb together.
>
> Prepare test data:
> ```
> drop table if exists people;
> drop type if exists person;
> CREATE TYPE person AS (
>     name text,
>     size int[],
>     meta jsonb[]
> );
>
> CREATE TABLE people (
>     p person
> );
>
> INSERT INTO people VALUES (ROW('Alice', array[10, 20], array['{"a":
> 30}'::jsonb, '{"a": 40}'::jsonb]));
> ```
>
> Then run the test:
> ```
> # old jsonb accessor works to extract a jsonb field from an array item of
> a composite field
> evantest=# select (p).meta[1]->'a' from people;
>  ?column?
> ----------
>  30
> (1 row)
>
> # dot notation also works
> evantest=# select (p).meta[1].a from people;
>  a
> ----
>  30
> (1 row)
>
> # but index accessor doesn’t work
> evantest=# select (p).meta[1]['a'] from people;
> ERROR:  invalid input syntax for type integer: "a"
> LINE 1: select (p).meta[1]['a'] from people;
>                            ^
>

This is the expected behavior for array subscripting, and my patch
doesn't change that. I don't think this is a problem. With or without
my patch, you can avoid the ERROR by adding parentheses:

test=# select ((p).meta[1])['a'] from people; meta ------ 30 (1 row)

On Mon, Sep 22, 2025 at 10:48 PM Chao Li <li.evan.chao@gmail.com> wrote:

> 2 - 0002
> ```
> + /* Collect leading A_Indices subscripts */
> + foreach(lc, indirection)
> + {
> + Node   *n = lfirst(lc);
> +
> + if (IsA(n, A_Indices))
> + {
> + A_Indices  *ai = (A_Indices *) n;
> +
> + subscriptlist = lappend(subscriptlist, n);
> + if (ai->is_slice)
> + isSlice = true;
> + }
> + else
> + break;
> ```
>
> We can break after “isSlice=true”.
>

Why? We still want to get the whole prefix list of A_Indices.

On Mon, Sep 22, 2025 at 10:48 PM Chao Li <li.evan.chao@gmail.com> wrote:

> 6 - 0002
> ```
> + /* This should not happen with well-behaved transform functions */
> + elog(ERROR, "subscripting transform function failed to consume any
> indirection elements”);
> ```
>
> I don’t see an existing error message uses “indirection” and “transform”.
> This error message looks more like a log message rather than a message to
> show to end users.
>

This is a defensive elog message that should not happen. So it is a
log message for developers. That said, I'm open to suggestions for
better wording.

The rest of your feedback I've made changes accordingly as you suggested.

Best,
Alex