Re: Virtual generated columns

Richard Guo <guofenglinux@gmail.com>

From: Richard Guo <guofenglinux@gmail.com>

To: jian he <jian.universality@gmail.com>

Cc: Alexander Lakhin <exclusion@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, Dean Rasheed <dean.a.rasheed@gmail.com>, Zhang Mingli <zmlpostgres@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>

Date: 2025-05-29T03:06:33Z

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

v1-0001-Expand-virtual-generated-columns-for-ALTER-COLUMN.patch (application/octet-stream) patch v1-0001

On Fri, May 16, 2025 at 5:35 PM jian he <jian.universality@gmail.com> wrote:
> we have used the USING expression in ATPrepAlterColumnType,
> ATColumnChangeRequiresRewrite.
> expanding it on ATPrepAlterColumnType seems to make more sense?
>
> @@ -14467,7 +14467,7 @@ ATPrepAlterColumnType(List **wqueue,
>                  */
>                 newval = (NewColumnValue *) palloc0(sizeof(NewColumnValue));
>                 newval->attnum = attnum;
> -               newval->expr = (Expr *) transform;
> +               newval->expr = (Expr *)
> expand_generated_columns_in_expr(transform, rel, 1);
>                 newval->is_generated = false;

Yeah, ATPrepAlterColumnType does seem like a better place.  But we
need to ensure that ATColumnChangeRequiresRewrite sees the expanded
version of the expression — your proposed change fails to do that.

Additionally, I think we also need to ensure that the virtual
generated columns are expanded before the expression is fed through
expression_planner, to ensure it can be successfully transformed into
an executable form.

Hence, the attached patch.

Thanks
Richard