Re: Bug: Rule actions see wrong values for generated columns (NEW.gen reads OLD value)

[Richard Guo]

On Mon, Apr 20, 2026 at 2:25 PM Richard Guo <guofengli...@gmail.com> wrote:
> Yeah, this is a better approach.  The change looks good to me.
>
> A nitpick: For the comment "The generated column expressions typically
> refer to new.attribute ...", maybe we can remove "typically", as
> generation expressions always refer to columns of the same relation.

I noticed a couple of issues after a further look.

1. The ReplaceVarsFromTargetList call on "gen_cols" fails to handle
hasSubLinks.  This can cause error if targetList contains SubLinks:

update t set a = (select max(a) from t);
ERROR:  replace_rte_variables inserted a SubLink, but has noplace to record it

2. The same bug fixed in this patch also exists in rule quals:

create table t (a int, b int generated always as (a *2));
insert into t values (1);

create rule rule_qual as on update to t where new.b > 100
  do instead nothing;

update t set a = 100;

select * from t;
  a  |  b
-----+-----
 100 | 200
(1 row)

I think we should apply the same fix to CopyAndAddInvertedQual.

Attached v3 fixes them.

- Richard

v3-0001-Fix-incorrect-NEW-references-to-generated-columns.patch
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