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Fix incorrect NEW references to generated columns in rule rewriting

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When a rule action or rule qualification references NEW.col where col
is a generated column (stored or virtual), the rewriter produces
incorrect results.

rewriteTargetListIU removes generated columns from the query's target
list, since stored generated columns are recomputed by the executor
and virtual ones store nothing.  However, ReplaceVarsFromTargetList
then cannot find these columns when resolving NEW references during
rule rewriting.  For UPDATE, the REPLACEVARS_CHANGE_VARNO fallback
redirects NEW.col to the original target relation, making it read the
pre-update value (same as OLD.col).  For INSERT,
REPLACEVARS_SUBSTITUTE_NULL replaces it with NULL.  Both are wrong
when the generated column depends on columns being modified.

Fix by building target list entries for generated columns from their
generation expressions, pre-resolving the NEW.attribute references
within those expressions against the query's targetlist, and passing
them together with the query's targetlist to ReplaceVarsFromTargetList.

Back-patch to all supported branches.  Virtual generated columns were
added in v18, so the back-patches in pre-v18 branches only handle
stored generated columns.

Reported-by: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>
Author: Richard Guo <guofenglinux@gmail.com>
Author: Dean Rasheed <dean.a.rasheed@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CAHg+QDexGTmCZzx=73gXkY2ZADS6LRhpnU+-8Y_QmrdTS6yUhA@mail.gmail.com
Backpatch-through: 14
This commit is contained in:
Richard Guo 2026-04-21 14:31:15 +09:00
parent 2d347f2cd7
commit 07b257189e
3 changed files with 187 additions and 5 deletions
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134
src/backend/rewrite/rewriteHandler.c
View file

@ -98,6 +98,7 @@ static List *matchLocks(CmdType event, RuleLock *rulelocks,
static Query *fireRIRrules(Query *parsetree, List *activeRIRs);
static bool view_has_instead_trigger(Relation view, CmdType event);
static Bitmapset *adjust_view_column_set(Bitmapset *cols, List *targetlist);
static List *get_generated_columns(Relation rel, int rt_index);
/*
@ -640,12 +641,45 @@ rewriteRuleAction(Query *parsetree,
if ((event == CMD_INSERT || event == CMD_UPDATE) &&
sub_action->commandType != CMD_UTILITY)
{
RangeTblEntry *new_rte = rt_fetch(new_varno, sub_action->rtable);
Relation new_rel;
List *gen_cols;
/*
* The target list does not contain entries for generated columns
* (they are removed by rewriteTargetListIU), so we must build entries
* for them here, so that new.gen_col can be rewritten correctly.
*/
new_rel = relation_open(new_rte->relid, NoLock);
gen_cols = get_generated_columns(new_rel, new_varno);
relation_close(new_rel, NoLock);
/*
* The generated column expressions refer to new.attribute, so they
* must be rewritten before they can be used as replacements.
*/
gen_cols = (List *)
ReplaceVarsFromTargetList((Node *) gen_cols,
new_varno,
0,
new_rte,
parsetree->targetList,
(event == CMD_UPDATE) ?
REPLACEVARS_CHANGE_VARNO :
REPLACEVARS_SUBSTITUTE_NULL,
current_varno,
&sub_action->hasSubLinks);
/*
* Now rewrite new.attribute in sub_action, using both the target list
* and the rewritten generated column expressions.
*/
sub_action = (Query *)
ReplaceVarsFromTargetList((Node *) sub_action,
new_varno,
0,
rt_fetch(new_varno, sub_action->rtable),
parsetree->targetList,
new_rte,
list_concat(gen_cols, parsetree->targetList),
(event == CMD_UPDATE) ?
REPLACEVARS_CHANGE_VARNO :
REPLACEVARS_SUBSTITUTE_NULL,
@ -2343,17 +2377,48 @@ CopyAndAddInvertedQual(Query *parsetree,
ChangeVarNodes(new_qual, PRS2_OLD_VARNO, rt_index, 0);
/* Fix references to NEW */
if (event == CMD_INSERT || event == CMD_UPDATE)
{
RangeTblEntry *rte = rt_fetch(rt_index, parsetree->rtable);
Relation rel;
List *gen_cols;
/*
* As in rewriteRuleAction, build entries for generated columns so
* that new.gen_col in the rule qualification can be rewritten
* correctly.
*/
rel = relation_open(rte->relid, NoLock);
gen_cols = get_generated_columns(rel, PRS2_NEW_VARNO);
relation_close(rel, NoLock);
/*
* The generated column expressions refer to new.attribute, so they
* must be rewritten before they can be used as replacements.
*/
gen_cols = (List *)
ReplaceVarsFromTargetList((Node *) gen_cols,
PRS2_NEW_VARNO,
0,
rte,
parsetree->targetList,
(event == CMD_UPDATE) ?
REPLACEVARS_CHANGE_VARNO :
REPLACEVARS_SUBSTITUTE_NULL,
rt_index,
&parsetree->hasSubLinks);
new_qual = ReplaceVarsFromTargetList(new_qual,
PRS2_NEW_VARNO,
0,
rt_fetch(rt_index,
parsetree->rtable),
parsetree->targetList,
rte,
list_concat(gen_cols,
parsetree->targetList),
(event == CMD_UPDATE) ?
REPLACEVARS_CHANGE_VARNO :
REPLACEVARS_SUBSTITUTE_NULL,
rt_index,
&parsetree->hasSubLinks);
}
/* And attach the fixed qual */
AddInvertedQual(parsetree, new_qual);
@ -4262,6 +4327,65 @@ RewriteQuery(Query *parsetree, List *rewrite_events, int orig_rt_length,
}
/*
* Get a table's generated columns
*
* Returns a list of TargetEntry, one for each generated column, containing
* the attribute numbers and generation expressions.
*/
static List *
get_generated_columns(Relation rel, int rt_index)
{
List *gen_cols = NIL;
TupleDesc tupdesc;
tupdesc = RelationGetDescr(rel);
if (tupdesc->constr && tupdesc->constr->has_generated_stored)
{
for (int i = 0; i < tupdesc->natts; i++)
{
Form_pg_attribute attr = TupleDescAttr(tupdesc, i);
if (attr->attgenerated == ATTRIBUTE_GENERATED_STORED)
{
Node *defexpr;
TargetEntry *te;
Oid attcollid;
defexpr = build_column_default(rel, i + 1);
if (defexpr == NULL)
elog(ERROR, "no generation expression found for column number %d of table \"%s\"",
i + 1, RelationGetRelationName(rel));
/*
* If the column definition has a collation and it is
* different from the collation of the generation expression,
* put a COLLATE clause around the expression.
*/
attcollid = attr->attcollation;
if (attcollid && attcollid != exprCollation(defexpr))
{
CollateExpr *ce = makeNode(CollateExpr);
ce->arg = (Expr *) defexpr;
ce->collOid = attcollid;
ce->location = -1;
defexpr = (Node *) ce;
}
ChangeVarNodes(defexpr, 1, rt_index, 0);
te = makeTargetEntry((Expr *) defexpr, i + 1, 0, false);
gen_cols = lappend(gen_cols, te);
}
}
}
return gen_cols;
}
/*
* QueryRewrite -
* Primary entry point to the query rewriter.

34
src/test/regress/expected/generated.out
View file

@ -1207,3 +1207,37 @@ CREATE TABLE gtest28b (LIKE gtest28a INCLUDING GENERATED);
c | integer | | |
x | integer | | | generated always as (b * 2) stored
-- rule actions referring to generated columns:
-- NEW.b in a rule action should reflect the generated column's new value
CREATE TABLE gtest_rule (a int, b int GENERATED ALWAYS AS (a * 2) STORED);
CREATE TABLE gtest_rule_log (op text, old_b int, new_b int);
CREATE RULE gtest_rule_upd AS ON UPDATE TO gtest_rule
DO ALSO INSERT INTO gtest_rule_log VALUES ('UPD', OLD.b, NEW.b);
CREATE RULE gtest_rule_ins AS ON INSERT TO gtest_rule
DO ALSO INSERT INTO gtest_rule_log VALUES ('INS', NULL, NEW.b);
INSERT INTO gtest_rule (a) VALUES (1);
UPDATE gtest_rule SET a = 10;
UPDATE gtest_rule SET a = (SELECT max(b) FROM gtest_rule);
SELECT * FROM gtest_rule_log;
op | old_b | new_b
-----+-------+-------
INS | | 2
UPD | 2 | 20
UPD | 20 | 40
(3 rows)
DROP RULE gtest_rule_upd ON gtest_rule;
DROP RULE gtest_rule_ins ON gtest_rule;
DROP TABLE gtest_rule_log;
-- rule quals referring to generated columns:
-- NEW.b in the rule qual should reflect the generated column's new value
CREATE RULE gtest_rule_qual AS ON UPDATE TO gtest_rule WHERE NEW.b > 100
DO INSTEAD NOTHING;
UPDATE gtest_rule SET a = 100;
SELECT * FROM gtest_rule;
a | b
----+----
20 | 40
(1 row)
DROP TABLE gtest_rule;

24
src/test/regress/sql/generated.sql
View file

@ -643,3 +643,27 @@ ALTER TABLE gtest28a DROP COLUMN a;
CREATE TABLE gtest28b (LIKE gtest28a INCLUDING GENERATED);
\d gtest28*
-- rule actions referring to generated columns:
-- NEW.b in a rule action should reflect the generated column's new value
CREATE TABLE gtest_rule (a int, b int GENERATED ALWAYS AS (a * 2) STORED);
CREATE TABLE gtest_rule_log (op text, old_b int, new_b int);
CREATE RULE gtest_rule_upd AS ON UPDATE TO gtest_rule
DO ALSO INSERT INTO gtest_rule_log VALUES ('UPD', OLD.b, NEW.b);
CREATE RULE gtest_rule_ins AS ON INSERT TO gtest_rule
DO ALSO INSERT INTO gtest_rule_log VALUES ('INS', NULL, NEW.b);
INSERT INTO gtest_rule (a) VALUES (1);
UPDATE gtest_rule SET a = 10;
UPDATE gtest_rule SET a = (SELECT max(b) FROM gtest_rule);
SELECT * FROM gtest_rule_log;
DROP RULE gtest_rule_upd ON gtest_rule;
DROP RULE gtest_rule_ins ON gtest_rule;
DROP TABLE gtest_rule_log;
-- rule quals referring to generated columns:
-- NEW.b in the rule qual should reflect the generated column's new value
CREATE RULE gtest_rule_qual AS ON UPDATE TO gtest_rule WHERE NEW.b > 100
DO INSTEAD NOTHING;
UPDATE gtest_rule SET a = 100;
SELECT * FROM gtest_rule;
DROP TABLE gtest_rule;