Horton

Re: Virtual generated columns

Richard Guo <guofenglinux@gmail.com>

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From: Richard Guo <guofenglinux@gmail.com>
To: Zhang Mingli <zmlpostgres@gmail.com>
Cc: jian he <jian.universality@gmail.com>, Peter Eisentraut <peter@eisentraut.org>, Dean Rasheed <dean.a.rasheed@gmail.com>, Alexander Lakhin <exclusion@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-02-11T09:15:24Z
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__.

On Tue, Feb 11, 2025 at 10:34 AM Richard Guo <guofenglinux@gmail.com> wrote:
> Yeah, I also feel that the virtual generated columns should adhere to
> outer join semantics, rather than being unconditionally replaced by
> the generation expressions.  But maybe I'm wrong.
>
> If that's the case, this incorrect-result issue isn't limited to
> constant expressions; it could also occur with non-strict ones.

It seems that outer-join removal does not work well with virtual
generated columns.

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

explain (costs off)
select t.a from t left join vt on t.a = vt.a where coalesce(vt.b, 1) = 1;
  QUERY PLAN
---------------
 Seq Scan on t
(1 row)

This plan does not seem correct to me.  The inner-rel attribute 'vt.b'
is used above the join, which means the join should not be removed.

explain (costs off)
select t.a from t left join vt on t.a = vt.a where coalesce(vt.b, 1) =
1 or t.a is null;
server closed the connection unexpectedly

For this query, an Assert in remove_rel_from_query() is hit.

I haven't looked into the details yet, but I suspect that both of
these issues are caused by our failure to mark the correct nullingrel
bits for the virtual generated columns.

Thanks
Richard