On Fri, 17 Apr 2026 at 21:04, SATYANARAYANA NARLAPURAM
<[email protected]> wrote:
>
> Hi hackers,
>
> UPDATE and DELETE with WHERE CURRENT OF cursor fail on tables that have
> virtual 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, which
> unconditionally errors on any CurrentOfExpr referencing the target relation.
> This appears to a check designed for view rewriting, where WHERE CURRENT OF
> cannot be translated through a view. However, virtual generated column (VGC)
> expansion also routes through this mutator. The rewriter's
> expand_generated_columns_internal() calls ReplaceVarsFromTargetList(), and
> the planner's expand_virtual_generated_columns() calls pullup_replace_vars(),
> which calls replace_rte_variables(). Since virtual generated columns use same
> mutator, while expanding virtual generated columns returns the same error
> even 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. The
> existing replace_rte_variables() is refactored into a static
> replace_rte_variables_internal() that accepts the flag, with two public
> wrappers: replace_rte_variables() (passes true, preserving existing behavior)
> and replace_rte_variables_ext() (exposes the flag). The same pattern is
> applied to ReplaceVarsFromTargetList() / ReplaceVarsFromTargetListExtended().
> In replace_rte_variables_mutator(), the CurrentOfExpr error is now
> conditional on context->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 adding 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
diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
new file mode 100644
index 84deed9..d984535
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -595,6 +595,14 @@ transformDeleteStmt(ParseState *pstate,
ACL_DELETE);
nsitem = pstate->p_target_nsitem;
+ /* disallow DELETE ... WHERE CURRENT OF on a view */
+ if (stmt->whereClause &&
+ IsA(stmt->whereClause, CurrentOfExpr) &&
+ pstate->p_target_relation->rd_rel->relkind == RELKIND_VIEW)
+ ereport(ERROR,
+ errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("WHERE CURRENT OF on a view is not implemented"));
+
/* there's no DISTINCT in DELETE */
qry->distinctClause = NIL;
@@ -2868,6 +2876,14 @@ transformUpdateStmt(ParseState *pstate,
true,
ACL_UPDATE);
+ /* disallow UPDATE ... WHERE CURRENT OF on a view */
+ if (stmt->whereClause &&
+ IsA(stmt->whereClause, CurrentOfExpr) &&
+ pstate->p_target_relation->rd_rel->relkind == RELKIND_VIEW)
+ ereport(ERROR,
+ errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("WHERE CURRENT OF on a view is not implemented"));
+
if (stmt->forPortionOf)
qry->forPortionOf = transformForPortionOfClause(pstate,
qry->resultRelation,
diff --git a/src/backend/rewrite/rewriteManip.c b/src/backend/rewrite/rewriteManip.c
new file mode 100644
index 4bf4aa0..9aa7ef6
--- a/src/backend/rewrite/rewriteManip.c
+++ b/src/backend/rewrite/rewriteManip.c
@@ -1514,25 +1514,6 @@ replace_rte_variables_mutator(Node *node
}
/* otherwise fall through to copy the var normally */
}
- else if (IsA(node, CurrentOfExpr))
- {
- CurrentOfExpr *cexpr = (CurrentOfExpr *) node;
-
- if (cexpr->cvarno == context->target_varno &&
- context->sublevels_up == 0)
- {
- /*
- * We get here if a WHERE CURRENT OF expression turns out to apply
- * to a view. Someday we might be able to translate the
- * expression to apply to an underlying table of the view, but
- * right now it's not implemented.
- */
- ereport(ERROR,
- (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
- errmsg("WHERE CURRENT OF on a view is not implemented")));
- }
- /* otherwise fall through to copy the expr normally */
- }
else if (IsA(node, Query))
{
/* Recurse into RTE subquery or not-yet-planned sublink subquery */
diff --git a/src/test/regress/expected/generated_virtual.out b/src/test/regress/expected/generated_virtual.out
new file mode 100644
index fc41c48..c238ef8
--- a/src/test/regress/expected/generated_virtual.out
+++ b/src/test/regress/expected/generated_virtual.out
@@ -1723,3 +1723,43 @@ select * from gtest33 where b is null;
reset constraint_exclusion;
drop table gtest33;
+create table gtest_cursor (id int primary key, a int, b int generated always as (a * 2) virtual);
+insert into gtest_cursor values (1, 10), (2, 20), (3, 30);
+-- UPDATE via cursor
+begin;
+declare cur1 cursor for select * from gtest_cursor order by id for update;
+fetch 1 from cur1;
+ id | a | b
+----+----+----
+ 1 | 10 | 20
+(1 row)
+
+update gtest_cursor set a = 99 where current of cur1;
+select * from gtest_cursor order by id;
+ id | a | b
+----+----+-----
+ 1 | 99 | 198
+ 2 | 20 | 40
+ 3 | 30 | 60
+(3 rows)
+
+commit;
+-- DELETE via cursor
+begin;
+declare cur2 cursor for select * from gtest_cursor order by id for update;
+fetch 1 from cur2;
+ id | a | b
+----+----+-----
+ 1 | 99 | 198
+(1 row)
+
+delete from gtest_cursor where current of cur2;
+select * from gtest_cursor order by id;
+ id | a | b
+----+----+----
+ 2 | 20 | 40
+ 3 | 30 | 60
+(2 rows)
+
+commit;
+drop table gtest_cursor;
diff --git a/src/test/regress/sql/generated_virtual.sql b/src/test/regress/sql/generated_virtual.sql
new file mode 100644
index 9b32413..5bab7d3
--- a/src/test/regress/sql/generated_virtual.sql
+++ b/src/test/regress/sql/generated_virtual.sql
@@ -906,3 +906,24 @@ select * from gtest33 where b is null;
reset constraint_exclusion;
drop table gtest33;
+
+create table gtest_cursor (id int primary key, a int, b int generated always as (a * 2) virtual);
+insert into gtest_cursor values (1, 10), (2, 20), (3, 30);
+
+-- UPDATE via cursor
+begin;
+declare cur1 cursor for select * from gtest_cursor order by id for update;
+fetch 1 from cur1;
+update gtest_cursor set a = 99 where current of cur1;
+select * from gtest_cursor order by id;
+commit;
+
+-- DELETE via cursor
+begin;
+declare cur2 cursor for select * from gtest_cursor order by id for update;
+fetch 1 from cur2;
+delete from gtest_cursor where current of cur2;
+select * from gtest_cursor order by id;
+commit;
+
+drop table gtest_cursor;
