Generated columns

This is an SQL-standard feature that allows creating columns that are
computed from expressions rather than assigned, similar to a view or
materialized view but on a column basis.

This implements one kind of generated column: stored (computed on
write).  Another kind, virtual (computed on read), is planned for the
future, and some room is left for it.

Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/b151f851-4019-bdb1-699e-ebab07d2f40a@2ndquadrant.com

3 files changed, 30 insertions, 3 deletions

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 979c3c212fd..cc222cb06cf 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -6570,8 +6570,9 @@ make_modifytable(PlannerInfo *root,
 
 		/*
 		 * Try to modify the foreign table directly if (1) the FDW provides
-		 * callback functions needed for that, (2) there are no row-level
-		 * triggers on the foreign table, and (3) there are no WITH CHECK
+		 * callback functions needed for that and (2) there are no local
+		 * structures that need to be run for each modified row: row-level
+		 * triggers on the foreign table, stored generated columns, WITH CHECK
 		 * OPTIONs from parent views.
 		 */
 		direct_modify = false;
@@ -6581,7 +6582,8 @@ make_modifytable(PlannerInfo *root,
 			fdwroutine->IterateDirectModify != NULL &&
 			fdwroutine->EndDirectModify != NULL &&
 			withCheckOptionLists == NIL &&
-			!has_row_triggers(subroot, rti, operation))
+			!has_row_triggers(subroot, rti, operation) &&
+			!has_stored_generated_columns(subroot, rti))
 			direct_modify = fdwroutine->PlanDirectModify(subroot, node, rti, i);
 		if (direct_modify)
 			direct_modify_plans = bms_add_member(direct_modify_plans, i);
diff --git a/src/backend/optimizer/util/inherit.c b/src/backend/optimizer/util/inherit.c
index 1d1e5060e26..d467a4826b0 100644
--- a/src/backend/optimizer/util/inherit.c
+++ b/src/backend/optimizer/util/inherit.c
@@ -280,6 +280,10 @@ expand_partitioned_rtentry(PlannerInfo *root, RangeTblEntry *parentrte,
 	if (!root->partColsUpdated)
 		root->partColsUpdated =
 			has_partition_attrs(parentrel, parentrte->updatedCols, NULL);
+	/*
+	 * There shouldn't be any generated columns in the partition key.
+	 */
+	Assert(!has_partition_attrs(parentrel, parentrte->extraUpdatedCols, NULL));
 
 	/*
 	 * If the partitioned table has no partitions, treat this as the
@@ -415,6 +419,8 @@ expand_single_inheritance_child(PlannerInfo *root, RangeTblEntry *parentrte,
 													 appinfo->translated_vars);
 		childrte->updatedCols = translate_col_privs(parentrte->updatedCols,
 													appinfo->translated_vars);
+		childrte->extraUpdatedCols = translate_col_privs(parentrte->extraUpdatedCols,
+														 appinfo->translated_vars);
 	}
 
 	/*
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index a0a7c5442de..2ebded8a954 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -2083,6 +2083,25 @@ has_row_triggers(PlannerInfo *root, Index rti, CmdType event)
 	return result;
 }
 
+bool
+has_stored_generated_columns(PlannerInfo *root, Index rti)
+{
+	RangeTblEntry *rte = planner_rt_fetch(rti, root);
+	Relation    relation;
+	TupleDesc	tupdesc;
+	bool        result = false;
+
+	/* Assume we already have adequate lock */
+	relation = heap_open(rte->relid, NoLock);
+
+	tupdesc = RelationGetDescr(relation);
+	result = tupdesc->constr && tupdesc->constr->has_generated_stored;
+
+	heap_close(relation, NoLock);
+
+	return result;
+}
+
 /*
  * set_relation_partition_info
  *