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From: Dean Rasheed <dean.a.rasheed@gmail.com>
Date: Sun, 19 Apr 2026 11:42:28 +0100
Message-ID: 
 <CAEZATCUyKUrL_4pDZ=pqL68BcWznoyuCqGS3-7sm-Lc_UxS9HQ@mail.gmail.com>
Subject: Re: [BUG]: WHERE CURRENT OF cursor fail on tables that have virtual
 generated columns
To: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Fri, 17 Apr 2026 at 21:04, SATYANARAYANA NARLAPURAM
<satyanarlapuram@gmail.com> wrote:
>
> Hi hackers,
>
> UPDATE and DELETE with WHERE CURRENT OF cursor fail on tables that have v=
irtual generated columns, erroring with "WHERE CURRENT OF on a view is not =
implemented" even though the target is a regular table, not a view.
>

Nice catch!

> Analysis:
> The bug stems from replace_rte_variables_mutator() in rewriteManip.c, whi=
ch unconditionally errors on any CurrentOfExpr referencing the target relat=
ion. This appears to a check designed for view rewriting, where WHERE CURRE=
NT OF cannot be translated through a view. However, virtual generated colum=
n (VGC) expansion also routes through this mutator. The rewriter's expand_g=
enerated_columns_internal() calls ReplaceVarsFromTargetList(), and the plan=
ner's expand_virtual_generated_columns() calls pullup_replace_vars(), which=
 calls replace_rte_variables(). Since virtual generated columns use same mu=
tator, while expanding virtual generated columns returns the same error eve=
n though the table is not a view and the cursor position is perfectly valid=
.
>
> The fix adds bool error_on_current_of to replace_rte_variables_context. T=
he existing replace_rte_variables() is refactored into a static replace_rte=
_variables_internal() that accepts the flag, with two public wrappers: repl=
ace_rte_variables() (passes true, preserving existing behavior) and replace=
_rte_variables_ext() (exposes the flag). The same pattern is applied to Rep=
laceVarsFromTargetList() / ReplaceVarsFromTargetListExtended(). In replace_=
rte_variables_mutator(), the CurrentOfExpr error is now conditional on cont=
ext->error_on_current_of. The two VGC expansion call sites pass false; all =
other callers pass true. The down side of this approach is that it is addin=
g additional public API.
>

Hmm, it seems to me that a much simpler fix is to check for use of
WHERE CURRENT OF on a view at parse time, and throw the error there.
Then the problematic rewriter check can simply be removed, as in the
attached v2 patch.

Regards,
Dean

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