Add support for MERGE ... WHEN NOT MATCHED BY SOURCE.

This allows MERGE commands to include WHEN NOT MATCHED BY SOURCE
actions, which operate on rows that exist in the target relation, but
not in the data source. These actions can execute UPDATE, DELETE, or
DO NOTHING sub-commands.

This is in contrast to already-supported WHEN NOT MATCHED actions,
which operate on rows that exist in the data source, but not in the
target relation. To make this distinction clearer, such actions may
now be written as WHEN NOT MATCHED BY TARGET.

Writing WHEN NOT MATCHED without specifying BY SOURCE or BY TARGET is
equivalent to writing WHEN NOT MATCHED BY TARGET.

Dean Rasheed, reviewed by Alvaro Herrera, Ted Yu and Vik Fearing.

Discussion: https://postgr.es/m/CAEZATCWqnKGc57Y_JanUBHQXNKcXd7r=0R4NEZUVwP+syRkWbA@mail.gmail.com

1 files changed, 25 insertions, 1 deletions

diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
index 7698bfa1a58..931b9c09bda 100644
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -134,6 +134,7 @@ preprocess_targetlist(PlannerInfo *root)
 	if (command_type == CMD_MERGE)
 	{
 		ListCell   *l;
+		List	   *vars;
 
 		/*
 		 * For MERGE, handle targetlist of each MergeAction separately. Give
@@ -144,7 +145,6 @@ preprocess_targetlist(PlannerInfo *root)
 		foreach(l, parse->mergeActionList)
 		{
 			MergeAction *action = (MergeAction *) lfirst(l);
-			List	   *vars;
 			ListCell   *l2;
 
 			if (action->commandType == CMD_INSERT)
@@ -182,6 +182,30 @@ preprocess_targetlist(PlannerInfo *root)
 			}
 			list_free(vars);
 		}
+
+		/*
+		 * Add resjunk entries for any Vars and PlaceHolderVars used in the
+		 * join condition that belong to relations other than the target.  We
+		 * don't expect to see any aggregates or window functions here.
+		 */
+		vars = pull_var_clause(parse->mergeJoinCondition,
+							   PVC_INCLUDE_PLACEHOLDERS);
+		foreach(l, vars)
+		{
+			Var		   *var = (Var *) lfirst(l);
+			TargetEntry *tle;
+
+			if (IsA(var, Var) && var->varno == result_relation)
+				continue;		/* don't need it */
+
+			if (tlist_member((Expr *) var, tlist))
+				continue;		/* already got it */
+
+			tle = makeTargetEntry((Expr *) var,
+								  list_length(tlist) + 1,
+								  NULL, true);
+			tlist = lappend(tlist, tle);
+		}
 	}
 
 	/*