v1-0001-fpo-inheritance-fix.patch

diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index dfd7b33a..30cf7698 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -1520,12 +1520,25 @@ ExecForPortionOfLeftovers(ModifyTableContext *context,
 	fcinfo->args[1].isnull = false;
 
 	/*
-	 * If there are partitions, we must insert into the root table, so we get
-	 * tuple routing. We already set up leftoverSlot with the root tuple
+	 * If the target is partitioned, we must insert into the root table so we
+	 * get tuple routing.  We already set up leftoverSlot with the root tuple
 	 * descriptor.
+	 *
+	 * For traditional inheritance (no partition tuple routing), we must
+	 * insert back into the same child table so that child-specific columns
+	 * are preserved.  In that case we need a leftover slot that matches the
+	 * child's tuple descriptor rather than the root's.
 	 */
-	if (resultRelInfo->ri_RootResultRelInfo)
+	if (resultRelInfo->ri_RootResultRelInfo &&
+		mtstate->mt_partition_tuple_routing)
 		resultRelInfo = resultRelInfo->ri_RootResultRelInfo;
+	else if (resultRelInfo->ri_RootResultRelInfo)
+	{
+		leftoverSlot =
+			ExecInitExtraTupleSlot(estate,
+								   RelationGetDescr(resultRelInfo->ri_RelationDesc),
+								   &TTSOpsVirtual);
+	}
 
 	/*
 	 * Insert a leftover for each value returned by the without_portion helper
@@ -1557,8 +1570,12 @@ ExecForPortionOfLeftovers(ModifyTableContext *context,
 			 * range column below. Convert oldtuple to the base table's format
 			 * if necessary. We need to insert temporal leftovers through the
 			 * root partition so they get routed correctly.
+			 *
+			 * For traditional inheritance (no partition routing), we keep the
+			 * child's tuple format so that child-specific columns are
+			 * preserved.
 			 */
-			if (map != NULL)
+			if (map != NULL && mtstate->mt_partition_tuple_routing)
 			{
 				leftoverSlot = execute_attr_map_slot(map->attrMap,
 													 oldtupleSlot,
diff --git a/src/test/regress/expected/for_portion_of.out b/src/test/regress/expected/for_portion_of.out
index 31f772c7..250e3653 100644
--- a/src/test/regress/expected/for_portion_of.out
+++ b/src/test/regress/expected/for_portion_of.out
@@ -2097,4 +2097,44 @@ SELECT * FROM temporal_partitioned_5 ORDER BY id, valid_at;
 (4 rows)
 
 DROP TABLE temporal_partitioned;
+-- UPDATE FOR PORTION OF with table inheritance
+-- Leftover rows must stay in the child table, preserving child-specific columns.
+CREATE TABLE fpo_inh_parent (
+  id int4range,
+  valid_at daterange,
+  name text
+);
+CREATE TABLE fpo_inh_child (
+  description text
+) INHERITS (fpo_inh_parent);
+INSERT INTO fpo_inh_child (id, valid_at, name, description) VALUES
+  ('[1,2)', '[2018-01-01,2019-01-01)', 'one', 'initial');
+-- Update targets the parent; the matching row lives in the child.
+UPDATE fpo_inh_parent FOR PORTION OF valid_at FROM '2018-04-01' TO '2018-10-01'
+  SET name = 'one^1';
+-- All three rows should be in the child, with description preserved.
+SELECT tableoid::regclass, * FROM fpo_inh_parent ORDER BY valid_at;
+   tableoid    |  id   |        valid_at         | name  
+---------------+-------+-------------------------+-------
+ fpo_inh_child | [1,2) | [2018-01-01,2018-04-01) | one
+ fpo_inh_child | [1,2) | [2018-04-01,2018-10-01) | one^1
+ fpo_inh_child | [1,2) | [2018-10-01,2019-01-01) | one
+(3 rows)
+
+SELECT * FROM fpo_inh_child ORDER BY valid_at;
+  id   |        valid_at         | name  | description 
+-------+-------------------------+-------+-------------
+ [1,2) | [2018-01-01,2018-04-01) | one   | initial
+ [1,2) | [2018-04-01,2018-10-01) | one^1 | initial
+ [1,2) | [2018-10-01,2019-01-01) | one   | initial
+(3 rows)
+
+-- No rows should have leaked into the parent.
+SELECT * FROM ONLY fpo_inh_parent ORDER BY valid_at;
+ id | valid_at | name 
+----+----------+------
+(0 rows)
+
+DROP TABLE fpo_inh_parent CASCADE;
+NOTICE:  drop cascades to table fpo_inh_child
 RESET datestyle;
diff --git a/src/test/regress/sql/for_portion_of.sql b/src/test/regress/sql/for_portion_of.sql
index d4062acf..bb7c8046 100644
--- a/src/test/regress/sql/for_portion_of.sql
+++ b/src/test/regress/sql/for_portion_of.sql
@@ -1365,4 +1365,30 @@ SELECT * FROM temporal_partitioned_5 ORDER BY id, valid_at;
 
 DROP TABLE temporal_partitioned;
 
+-- UPDATE FOR PORTION OF with table inheritance
+-- Leftover rows must stay in the child table, preserving child-specific columns.
+
+CREATE TABLE fpo_inh_parent (
+  id int4range,
+  valid_at daterange,
+  name text
+);
+CREATE TABLE fpo_inh_child (
+  description text
+) INHERITS (fpo_inh_parent);
+INSERT INTO fpo_inh_child (id, valid_at, name, description) VALUES
+  ('[1,2)', '[2018-01-01,2019-01-01)', 'one', 'initial');
+
+-- Update targets the parent; the matching row lives in the child.
+UPDATE fpo_inh_parent FOR PORTION OF valid_at FROM '2018-04-01' TO '2018-10-01'
+  SET name = 'one^1';
+
+-- All three rows should be in the child, with description preserved.
+SELECT tableoid::regclass, * FROM fpo_inh_parent ORDER BY valid_at;
+SELECT * FROM fpo_inh_child ORDER BY valid_at;
+-- No rows should have leaked into the parent.
+SELECT * FROM ONLY fpo_inh_parent ORDER BY valid_at;
+
+DROP TABLE fpo_inh_parent CASCADE;
+
 RESET datestyle;