Re: Virtual generated columns

Richard Guo <guofenglinux@gmail.com>

From: Richard Guo <guofenglinux@gmail.com>

To: Dean Rasheed <dean.a.rasheed@gmail.com>

Cc: Peter Eisentraut <peter@eisentraut.org>, jian he <jian.universality@gmail.com>, Zhang Mingli <zmlpostgres@gmail.com>, Alexander Lakhin <exclusion@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>

Date: 2025-02-18T13:12:31Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Expand virtual generated columns for ALTER COLUMN TYPE
- 5069fef1cfae 18.0 landed
Eliminate code duplication in replace_rte_variables callbacks
- 363a6e8c6fcf 18.0 landed
Expand virtual generated columns in the planner
- 1e4351af329f 18.0 landed
Virtual generated columns
- 83ea6c54025b 18.0 landed
Additional tests for stored generated columns
- 41084409f635 18.0 landed
Improve generated_stored test
- 44b61efb7928 18.0 landed
- 86749ea3b766 18.0 landed
Fix handling of CREATE DOMAIN with GENERATED constraint syntax
- 84a67725cd11 18.0 landed
Add pg_constraint rows for not-null constraints
- 14e87ffa5c54 18.0 cited
Put generated_stored test objects in a schema
- 894be11adfa6 18.0 landed
Rename regress test generated to generated_stored
- b9ed4969250d 18.0 landed
Small code simplification
- 7ff9afbbd1df 18.0 landed
Remove useless code
- e26d313bad92 18.0 landed
Remove useless initializations
- da2aeba8f533 18.0 landed
doc: Clarify that pg_attrdef also stores generation expressions
- da486d360103 18.0 landed
Clean out column-level pg_init_privs entries when dropping tables.
- 76618097a6c0 17.0 cited
Re-implement the ereport() macro using __VA_ARGS__.
- e3a87b4991cc 13.0 cited

Attachments

v2-0001-Expand-virtual-generated-columns-in-planner.patch (application/octet-stream) patch v2-0001

On Tue, Feb 18, 2025 at 7:09 PM Richard Guo <guofenglinux@gmail.com> wrote:
> It seems to me that, for a relation in the rangetable that has virtual
> generated columns, we can consider it a subquery to some extent.  For
> instance, suppose we have a query:
>
> select ... from ... join t on ...;
>
> and suppose t.b is a virtual generated column.  We can consider this
> query as:
>
> select ... from ... join (select a, expr() as b from t) as t on ...;
>
> In this sense, I'm wondering if we can leverage the
> pullup_replace_vars architecture to expand the virtual generated
> columns.  I believe this would help avoid a lot of duplicate code with
> pullup_replace_vars_callback.

I had a try with this idea, and attached is what I came up with.  It
fixes all the mentioned issues but still requires significant
refinement, particularly due to the lack of comments.  By leveraging
the pullup_replace_vars architecture to expand the virtual generated
columns, it saves a lot of duplicate code.

Thanks
Richard