Horton

Re: Virtual generated columns

jian he <jian.universality@gmail.com>

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From: jian he <jian.universality@gmail.com>
To: Dean Rasheed <dean.a.rasheed@gmail.com>
Cc: Peter Eisentraut <peter@eisentraut.org>, Richard Guo <guofenglinux@gmail.com>, Zhang Mingli <zmlpostgres@gmail.com>, Alexander Lakhin <exclusion@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-02-17T06:48:18Z
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 →

  1. Expand virtual generated columns for ALTER COLUMN TYPE

  2. Eliminate code duplication in replace_rte_variables callbacks

  3. Expand virtual generated columns in the planner

  4. Virtual generated columns

  5. Additional tests for stored generated columns

  6. Improve generated_stored test

  7. Fix handling of CREATE DOMAIN with GENERATED constraint syntax

  8. Add pg_constraint rows for not-null constraints

  9. Put generated_stored test objects in a schema

  10. Rename regress test generated to generated_stored

  11. Small code simplification

  12. Remove useless code

  13. Remove useless initializations

  14. doc: Clarify that pg_attrdef also stores generation expressions

  15. Clean out column-level pg_init_privs entries when dropping tables.

  16. Re-implement the ereport() macro using __VA_ARGS__.

Attachments

On Sat, Feb 15, 2025 at 8:37 PM Dean Rasheed <dean.a.rasheed@gmail.com> wrote:
>
> On Fri, 14 Feb 2025 at 10:59, Peter Eisentraut <peter@eisentraut.org> wrote:
> >
> > On 13.02.25 14:06, jian he wrote:
> > > I didn't solve the out join semantic issue.
> > > i am wondering, can we do the virtual generated column expansion in
> > > the rewrite stage as is,
> > > and wrap the expressions in PHVs if the virtual generated
> > > columns come from the nullable side of an outer join.
> >
> > PlaceHolderVar looks like a fitting mechanism for this.  But it's so far
> > a planner node, so it might take some additional consideration if we
> > want to expand where it's used.
>
> It seems pretty baked into how PHVs work that they should only be
> added by the planner, so I think that I agree with Richard -- virtual
> generated columns probably have to be expanded in the planner rather
> than the rewriter.
>
> > Maybe a short-term fix would be to error out if we find ourselves about
> > to expand a Var with varnullingrels != NULL.  That would mean you
> > couldn't use a virtual generated column on the nullable output side of
> > an outer join, which is annoying but not fatal, and we could fix it
> > incrementally later.
>
> I think that would be rather a sad limitation to have. It would be
> nice to have this fully working for the next release.
>
error out seems not that hard, IMHO.
i think, we still have time to figure out how to make it fully working in v18.

> Attached is a rough patch that moves the expansion of virtual
> generated columns to the planner. It needs a lot more testing (and
> some regression tests), but it does seem to fix all the issues
> mentioned in this thread.
>
I will review it later.
In the meantime,
I also came up with my patch (including tests) that solves all the issues.