Horton

Re: Virtual generated columns

Richard Guo <guofenglinux@gmail.com>

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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: 2025-02-22T14:55:41Z
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 22, 2025 at 2:35 AM Dean Rasheed <dean.a.rasheed@gmail.com> wrote:
> On Fri, 21 Feb 2025 at 06:16, Richard Guo <guofenglinux@gmail.com> wrote:
> > * The expansion of virtual generated columns occurs after subquery
> > pullup, which can lead to issues.  This was an oversight on my part.
> > Initially, I believed it wasn't possible for an RTE_RELATION RTE to
> > have 'lateral' set to true, so I assumed it would be safe to expand
> > virtual generated columns after subquery pullup.  However, upon closer
> > look, this doesn't seem to be the case: if a subquery had a LATERAL
> > marker, that would be propagated to any of its child RTEs, even for
> > RTE_RELATION child RTE if this child rel has sampling info (see
> > pull_up_simple_subquery).
>
> Ah yes. That matches my initial instinct, which was to expand virtual
> generated columns early in the planning process, but I didn't properly
> understand why that was necessary.

After chewing on this point for a bit longer, I think the virtual
generated columns should be expanded after we have pulled up any
SubLinks within the query's quals; otherwise any virtual generated
column references within the SubLinks that should be transformed into
joins wouldn't get expanded.  As an example, please consider:

create table t (a int, b int);
create table vt (a int, b int generated always as (a * 2));

insert into t values (1, 1);
insert into vt values (1);

# select 1 from t t1 where exists
   (select 1 from vt where exists
    (select t1.a from t t2 where vt.b = 2));
ERROR:  unexpected virtual generated column reference

> LGTM aside from a comment in fireRIRrules() that needed updating and a
> minor issue in the callback function: when deciding whether to wrap
> newnode in a ReturningExpr, if newnode is a Var, it should now compare
> its varlevelsup with 0, not var->varlevelsup, since newnode hasn't had
> its varlevelsup adjusted at that point.

Nice catch.

Attached are the updated patches to fix all the mentioned issues.  I
plan to push them early next week after staring at the code for a bit
longer, barring any objections.

Thanks
Richard