Re: Extract numeric filed in JSONB more effectively - Mailing list pgsql-hackers

On Tue, Apr 7, 2026 at 5:00 PM Andy Fan <zhihuifan1213@163.com> wrote:

Haibo Yan <tristan.yim@gmail.com> writes:

Hi Haibo,

> I agree that if this approach is extended to the full matrix naively,
> duplication will become a real issue.

Could you summary how it would be? I think it would be helpful for
others to review.  Otherwise every reviewer needs to count them many
times.

--
Best Regards
Andy Fan

Hi Andy,
Sure.

My current thought is to extend it in stages, rather than trying to solve the full matrix in a single patch.

A rough plan would be:

1. Keep the current stage-1 patch small and validate the basic approach first

• jsonb_object_field / -> / equivalent subscripting form

• casts to numeric and bool

• support-function rewrite directly to explicit typed extractor functions

2. Extend target types before extending extractor families

• add int4 / int8 / float8 for the same object-field family first

• keep the SQL-visible rewrite targets explicit, e.g.

  • jsonb_object_field_int4

  • jsonb_object_field_int8

  • jsonb_object_field_float8

• avoid the previous numeric-intermediate rewrite shape

3. Then extend to other extractor families with the same overall pattern

• likely starting with jsonb_array_element and jsonb_extract_path

• and possibly jsonb_path_query_first later

• each family would still rewrite to explicit typed extractor entry points, e.g.

  • jsonb_array_element_numeric

  • jsonb_extract_path_bool

  • jsonb_path_query_first_int4

4. Keep duplication manageable by sharing the implementation underneath

• keep the SQL/catalog-level rewrite targets explicit for readability and reviewability

• but factor the C implementation into:

  • extractor-family lookup helpers

  • target-type conversion helpers

  • thin wrappers, possibly generated with small macros

So the idea would be: explicit rewrite targets at the SQL/catalog level, but shared lookup/conversion code underneath, instead of going back to the earlier start/finish/internal pipeline.

I agree that if this is extended naively across the full matrix, duplication will become a real issue. My reason for keeping the current patch narrow is that I wanted to first validate this simpler rewrite shape on a small subset before deciding how best to scale it further.

Regards,

Haibo

Hi all,

Following up on our previous discussion, I want to clarify the current patch plan together with the updated first patch.

Earlier I described this work roughly as a 4-patch line. After iterating on the implementation and trying to keep each step reviewable, I now think the cleaner split is a 5-patch series:

1. object-field casts to scalar types

2. array-element casts to scalar types

3. extract-path casts to scalar types

4. multi-subscript casts via extract-path lowering

5. jsonpath-first casts to scalar types (jsonb_path_query_first and _tz)

The overall design is unchanged: use the cast function’s support hook to recognize cast(extract(...)) over scalar-returning jsonb extraction functions, and rewrite that directly to explicit typed extractor calls.

Supported target types remain:

• numeric
• bool
• int4
• int8
• float8

One point I also want to make explicit is that I do not plan to include jsonb_path_query in this series.

After looking at it more carefully, I do not think it fits the same model as the rest of the series. The patches here are all about scalar-returning extraction functions, where the cast prosupport hook can see and rewrite a scalar expression pair. jsonb_path_query is set-returning, so optimizing casts over it would likely need a different mechanism, probably at planner or executor level, rather than one more patch in this prosupport-based series.

Attached here is the updated first patch in the current plan.

This patch covers object-field extraction only:

• jsonb_object_field
• -> with text key
• key subscripting

and rewrites casts to:

• numeric
• bool
• int4
• int8
• float8

to direct typed extractor calls.

Thanks again for the earlier comments. I plan to send the remaining patches in follow-up emails in the order above.

Regards,