merge command - GSoC progress

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 2f33fdb..56c13ee 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -171,6 +171,7 @@ standard_ExecutorStart(QueryDesc *queryDesc, int eflags)
 		case CMD_INSERT:
 		case CMD_DELETE:
 		case CMD_UPDATE:
+		case CMD_MERGE:	
 			estate->es_output_cid = GetCurrentCommandId(true);
 			break;
 
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index f4cc7d9..2d1a4e7 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -153,6 +153,11 @@ ExecInitNode(Plan *node, EState *estate, int eflags)
 													   estate, eflags);
 			break;
 
+		case T_MergeAction:
+			result = (PlanState *) ExecInitMergeAction((MergeAction*) node,
+													   estate, eflags);
+			break;
+			
 		case T_Append:
 			result = (PlanState *) ExecInitAppend((Append *) node,
 												  estate, eflags);
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 8619ce3..c549d7e 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -583,6 +583,116 @@ lreplace:;
 }
 
 
+static TupleTableSlot *
+ExecMerge(ItemPointer tupleid,
+		   TupleTableSlot *slot,
+		   TupleTableSlot *planSlot,
+		   ModifyTableState *node,
+		   EState *estate)
+{
+
+	TupleTableSlot *actslot = NULL;
+	TupleTableSlot *res = NULL;
+	ListCell *each;
+
+	/*
+	*	try the merge actions one by one
+	*/
+	foreach(each, node->mergeActPstates)
+	{
+		ModifyTableState *actpstate;
+
+		PlanState *pstate; 
+
+		ExprContext *econtext;
+
+		
+		actpstate = (ModifyTableState *)lfirst(each);
+		
+		Assert(actpstate->mt_nplans == 1);
+
+		pstate = actpstate->mt_plans[0];
+
+		/*
+		*	If tupleid == NULL, it is a NOT MATCHED case, in which we can only do INSERT action
+		*	If tupleid != NULL, it is a MATCHED case, in which we can only do UPDATE or DELETE action
+		*/
+		
+		if((tupleid == NULL && actpstate->operation != CMD_INSERT) ||
+			(tupleid != NULL && actpstate->operation == CMD_INSERT))
+		{
+			continue;
+		}
+
+		/*
+		*	Setup the expression context
+		*/
+		econtext = pstate->ps_ExprContext;
+
+		/*
+		If the action has an additional qual, which is not satisfied, skip it
+		*/	
+		
+		if(pstate->qual) 
+		{	
+
+			bool qualres;
+			
+			ResetExprContext(econtext);
+		
+			econtext->ecxt_scantuple = slot;
+			econtext->ecxt_outertuple = planSlot;
+
+			 if(!ExecQual(pstate->qual, econtext,false))
+				continue;
+		}
+
+		/*
+		*	Now we start to exec this action. Firstly , project the result tuple slot. 
+		*	The merge action result slot is projected in the same way as a returning slot. 
+		*	so we call ExecProcessReturning() directly here.
+		*/
+		if(actpstate->operation != CMD_DELETE)
+			actslot = ExecProcessReturning(pstate->ps_ProjInfo, slot, planSlot);
+	
+			
+		switch (actpstate->operation)
+		{
+			case CMD_INSERT:
+				res = ExecInsert(actslot, planSlot, estate);
+				break;
+			case CMD_UPDATE:
+				res = ExecUpdate(tupleid,
+							actslot,
+							planSlot,
+							&actpstate->mt_epqstate,
+							estate);
+				break;
+			case CMD_DELETE:
+				res = ExecDelete(tupleid, 
+							planSlot, 
+							&actpstate->mt_epqstate,
+							estate);
+				break;
+			default:
+				elog(ERROR, "unknown merge action type");
+				break;
+		}
+
+
+		/*
+		* The current action is executed, no need to do the remain actions
+		*/	
+		return res;
+	}
+
+	/*
+	* Here, no action is taken. Let's pass this slot
+	*/	
+	return NULL;
+	
+}
+
 /*
  * Process BEFORE EACH STATEMENT triggers
  */
@@ -603,6 +713,9 @@ fireBSTriggers(ModifyTableState *node)
 			ExecBSDeleteTriggers(node->ps.state,
 								 node->ps.state->es_result_relations);
 			break;
+		case CMD_MERGE:
+			printf("not sure about the BS triggers of merge\n");
+			break;
 		default:
 			elog(ERROR, "unknown operation");
 			break;
@@ -629,6 +742,9 @@ fireASTriggers(ModifyTableState *node)
 			ExecASDeleteTriggers(node->ps.state,
 								 node->ps.state->es_result_relations);
 			break;
+		case CMD_MERGE:
+			printf("not sure about the AS triggers of merge\n");
+			break;	
 		default:
 			elog(ERROR, "unknown operation");
 			break;
@@ -708,20 +824,34 @@ ExecModifyTable(ModifyTableState *node)
 			/*
 			 * extract the 'ctid' junk attribute.
 			 */
-			if (operation == CMD_UPDATE || operation == CMD_DELETE)
+			if (operation == CMD_UPDATE || operation == CMD_DELETE || operation == CMD_MERGE)
 			{
 				Datum		datum;
 				bool		isNull;
 
 				datum = ExecGetJunkAttribute(slot, junkfilter->jf_junkAttNo,
 											 &isNull);
-				/* shouldn't ever get a null result... */
+				
 				if (isNull)
-					elog(ERROR, "ctid is NULL");
-
-				tupleid = (ItemPointer) DatumGetPointer(datum);
-				tuple_ctid = *tupleid;	/* be sure we don't free the ctid!! */
-				tupleid = &tuple_ctid;
+				{
+					/*
+					*	shouldn't ever get a null result for update and delete. 
+					*	Merge command will get a null ctid if in "NOT MATCHED" case
+					*/
+					if(operation != CMD_MERGE)
+						elog(ERROR, "ctid is NULL");
+					else
+						tupleid = NULL;
+				}	
+				else
+				{
+				
+					tupleid = (ItemPointer) DatumGetPointer(datum);
+					
+					tuple_ctid = *tupleid;	/* be sure we don't free the ctid!! */
+					tupleid = &tuple_ctid;
+					
+				}
 			}
 
 			/*
@@ -744,6 +874,11 @@ ExecModifyTable(ModifyTableState *node)
 				slot = ExecDelete(tupleid, planSlot,
 								  &node->mt_epqstate, estate);
 				break;
+			case CMD_MERGE:
+				slot = ExecMerge(tupleid, slot, planSlot,
+								  node, estate);
+				break;	
+				
 			default:
 				elog(ERROR, "unknown operation");
 				break;
@@ -771,6 +906,93 @@ ExecModifyTable(ModifyTableState *node)
 	return NULL;
 }
 
+
+
+
+
+
+
+
+/*
+*	When init a merge plan, we also need init its action plans. 
+*	However, these action plans are "pure" plans. We only want to handle the tlist and qual
+*	Thus, the return result is a plain "PlanState". We dont have a MeregeActionState kind of thing.
+*/
+PlanState *
+ExecInitMergeAction(MergeAction *node, EState *estate, int eflags)
+{
+	PlanState *result;
+	
+	/*
+	 * do nothing when we get to the end of a leaf on tree.
+	 */
+	if (node == NULL)
+		return NULL;
+
+		
+	/*
+	 * create state structure
+	 */
+	result = makeNode(PlanState);
+	result->plan = (Plan *)node;
+	result->state = estate;
+
+	/*
+	 * tuple table initialization
+	 */
+	ExecInitResultTupleSlot(estate, result);
+
+
+	
+	/*
+	 * initialize tuple type and projection info
+	 */
+	ExecAssignResultTypeFromTL(result);
+
+		
+	/*
+	 * Miscellaneous initialization
+	 *
+	 * create expression context for node
+	 */
+	 
+	ExecAssignExprContext(estate, result);
+
+
+	/*
+	 * initialize child expressions
+	 */
+	result->targetlist = (List *)
+		ExecInitExpr((Expr *) node->plan.targetlist,  result);
+
+	
+	result->qual = (List *)
+		ExecInitExpr((Expr *) node->plan.qual, result);
+
+	
+	/*
+	* init the projection information
+	*/
+	ExecAssignProjectionInfo(result, NULL);
+
+/*
+printf("before check plan output for merge actio \n");	
+if(estate->es_result_relation_info == NULL)
+	printf("re infro is null\n");
+
+if(estate->es_result_relation_info->ri_RelationDesc == NULL)
+	printf("r relation desc is nUll\n");
+	ExecCheckPlanOutput(estate->es_result_relation_info->ri_RelationDesc,
+							node->targetlist);
+printf("AFTER check plan output for merge actio \n");	
+*/
+	return result;
+}
+
+
+
+
+
 /* ----------------------------------------------------------------
  *		ExecInitModifyTable
  * ----------------------------------------------------------------
@@ -786,7 +1008,9 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	Plan	   *subplan;
 	ListCell   *l;
 	int			i;
+	bool 		isMergeAction = false;
 
+	
 	/* check for unsupported flags */
 	Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
@@ -797,7 +1021,6 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	 */
 	if (estate->es_epqTuple != NULL)
 		elog(ERROR, "ModifyTable should not be called during EvalPlanQual");
-
 	/*
 	 * create state structure
 	 */
@@ -826,12 +1049,18 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	foreach(l, node->plans)
 	{
 		subplan = (Plan *) lfirst(l);
+		if(IsA(subplan, MergeAction))
+			isMergeAction = true;
+		
 		mtstate->mt_plans[i] = ExecInitNode(subplan, estate, eflags);
+
 		estate->es_result_relation_info++;
 		i++;
 	}
+	
 	estate->es_result_relation_info = NULL;
 
+	
 	/* select first subplan */
 	mtstate->mt_whichplan = 0;
 	subplan = (Plan *) linitial(node->plans);
@@ -955,7 +1184,9 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 				break;
 			case CMD_UPDATE:
 			case CMD_DELETE:
-				junk_filter_needed = true;
+			case CMD_MERGE:	
+				if(!isMergeAction)
+					junk_filter_needed = true;
 				break;
 			default:
 				elog(ERROR, "unknown operation");
@@ -973,15 +1204,16 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 				if (operation == CMD_INSERT || operation == CMD_UPDATE)
 					ExecCheckPlanOutput(resultRelInfo->ri_RelationDesc,
 										subplan->targetlist);
-
+				
 				j = ExecInitJunkFilter(subplan->targetlist,
 							resultRelInfo->ri_RelationDesc->rd_att->tdhasoid,
 									   ExecInitExtraTupleSlot(estate));
 
-				if (operation == CMD_UPDATE || operation == CMD_DELETE)
+				if (operation == CMD_UPDATE || operation == CMD_DELETE || operation == CMD_MERGE)
 				{
 					/* For UPDATE/DELETE, find the ctid junk attr now */
 					j->jf_junkAttNo = ExecFindJunkAttribute(j, "ctid");
+
 					if (!AttributeNumberIsValid(j->jf_junkAttNo))
 						elog(ERROR, "could not find junk ctid column");
 				}
@@ -1006,6 +1238,21 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	if (estate->es_trig_tuple_slot == NULL)
 		estate->es_trig_tuple_slot = ExecInitExtraTupleSlot(estate);
 
+	
+	/*
+	* for the merge actions, we need to similar things as above
+	*/
+
+	foreach(l, node->mergeActPlan)
+	{
+		PlanState *actpstate = ExecInitNode((Plan *)lfirst(l),  estate, 0);
+		/*
+		* put the pstates of each action into ModifyTableState
+		*/
+		mtstate->mergeActPstates = lappend(mtstate->mergeActPstates, actpstate);
+		
+	}
+	
 	return mtstate;
 }
 
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 93dcef5..f0be5e8 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -176,6 +176,7 @@ _copyModifyTable(ModifyTable *from)
 	COPY_NODE_FIELD(returningLists);
 	COPY_NODE_FIELD(rowMarks);
 	COPY_SCALAR_FIELD(epqParam);
+	COPY_NODE_FIELD(mergeActPlan);
 
 	return newnode;
 }
@@ -2273,6 +2274,10 @@ _copyQuery(Query *from)
 	COPY_NODE_FIELD(rowMarks);
 	COPY_NODE_FIELD(setOperations);
 
+	COPY_SCALAR_FIELD(isMergeAction);
+	/*merge action list*/
+	COPY_NODE_FIELD(mergeActQry); 
+
 	return newnode;
 }
 
@@ -2343,6 +2348,64 @@ _copySelectStmt(SelectStmt *from)
 	return newnode;
 }
 
+
+static MergeStmt *
+_copyMergeStmt(MergeStmt *from)
+{
+	MergeStmt *newnode = makeNode(MergeStmt);
+
+	COPY_NODE_FIELD(relation);
+	COPY_NODE_FIELD(source);
+	COPY_NODE_FIELD(matchCondition);
+	COPY_NODE_FIELD(actions);
+	
+	return newnode;
+	
+}
+
+
+static MergeConditionAction *
+_copyMergeConditionAction(MergeConditionAction *from)
+{
+	MergeConditionAction *newnode = makeNode(MergeConditionAction);
+
+	COPY_SCALAR_FIELD(match);
+	COPY_NODE_FIELD(condition);
+	COPY_NODE_FIELD(action);
+
+	return newnode;
+}
+
+static MergeUpdate *
+_copyMergeUpdate(MergeUpdate *from)
+{
+	MergeUpdate *newNode = (MergeUpdate *)_copyUpdateStmt((UpdateStmt *) from);
+	newNode->type = T_MergeUpdate;
+
+	return newNode;
+}
+
+static MergeInsert *
+_copyMergeInsert(MergeInsert *from)
+{
+	MergeInsert *newNode = (MergeInsert *)_copyInsertStmt((InsertStmt *) from);
+	newNode->type = T_MergeInsert;
+
+	return newNode;
+}
+
+
+static MergeDelete *
+_copyMergeDelete(MergeDelete *from)
+{
+	MergeDelete *newNode = (MergeDelete *)_copyDeleteStmt((DeleteStmt *) from);
+	newNode->type = T_MergeDelete;
+
+	return newNode;
+}
+
+
+
 static SetOperationStmt *
 _copySetOperationStmt(SetOperationStmt *from)
 {
@@ -3902,7 +3965,22 @@ copyObject(void *from)
 			break;
 		case T_SelectStmt:
 			retval = _copySelectStmt(from);
-			break;
+			break;		
+		case T_MergeStmt:
+			retval = _copyMergeStmt(from);
+			break;			
+		case T_MergeConditionAction:
+			retval = _copyMergeConditionAction(from);
+			break;	
+		case T_MergeUpdate:
+			retval = _copyMergeUpdate(from);
+			break;
+		case T_MergeInsert:
+			retval = _copyMergeInsert(from);
+			break;	
+		case T_MergeDelete:
+			retval = _copyMergeDelete(from);
+			break;	
 		case T_SetOperationStmt:
 			retval = _copySetOperationStmt(from);
 			break;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 5d83727..572f6df 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -878,6 +878,7 @@ _equalQuery(Query *a, Query *b)
 	COMPARE_NODE_FIELD(rowMarks);
 	COMPARE_NODE_FIELD(setOperations);
 
+	COMPARE_SCALAR_FIELD(isMergeAction);
 	return true;
 }
 
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 79baf4f..4b3dd60 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -331,6 +331,7 @@ _outModifyTable(StringInfo str, ModifyTable *node)
 	WRITE_NODE_FIELD(returningLists);
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_INT_FIELD(epqParam);
+	WRITE_NODE_FIELD(mergeActPlan);
 }
 
 static void
@@ -2019,9 +2020,52 @@ _outQuery(StringInfo str, Query *node)
 	WRITE_NODE_FIELD(limitCount);
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_NODE_FIELD(setOperations);
+	WRITE_BOOL_FIELD(isMergeAction);
+	WRITE_NODE_FIELD(mergeActQry);
+}
+
+
+static void
+_outMergeConditionAction(StringInfo str, MergeConditionAction *node)
+{
+	WRITE_NODE_TYPE("MERGECONDITIONACTION");
+
+	WRITE_BOOL_FIELD(match);
+	
+	WRITE_NODE_FIELD(condition);
+	WRITE_NODE_FIELD(action);
+
+
 }
 
 static void
+_outMergeStmt(StringInfo str, MergeStmt *node)
+{
+	WRITE_NODE_TYPE("MERGESTMT");
+
+	WRITE_NODE_FIELD(relation);
+	WRITE_NODE_FIELD(source);
+	WRITE_NODE_FIELD(matchCondition);
+	WRITE_NODE_FIELD(actions);
+
+}
+
+static void 
+_outDeleteStmt(StringInfo str, DeleteStmt *node)
+{
+	WRITE_NODE_TYPE("DELETESTMT");
+
+	WRITE_NODE_FIELD(relation);
+	WRITE_NODE_FIELD(usingClause);
+	WRITE_NODE_FIELD(whereClause);
+	WRITE_NODE_FIELD(returningList);
+
+
+}
+
+
+
+static void
 _outSortGroupClause(StringInfo str, SortGroupClause *node)
 {
 	WRITE_NODE_TYPE("SORTGROUPCLAUSE");
@@ -2905,6 +2949,17 @@ _outNode(StringInfo str, void *obj)
 				_outXmlSerialize(str, obj);
 				break;
 
+			case T_MergeStmt:
+				_outMergeStmt(str, obj);
+				break;
+			case T_MergeConditionAction:
+				_outMergeConditionAction(str,obj);
+				break;
+			case T_DeleteStmt:
+				_outDeleteStmt(str,obj);
+				break;
+					
+
 			default:
 
 				/*
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 3950ab4..f8ab23f 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -565,6 +565,26 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 											 returningLists,
 											 rowMarks,
 											 SS_assign_special_param(root));
+
+			/*do a simple plan for each actions in the merge command.
+			*put them in mergeActPlan list;
+			*/
+			if(parse->commandType == CMD_MERGE)
+			{
+				ListCell *l;
+				ModifyTable *top_plan = (ModifyTable *)plan;
+				foreach(l, parse->mergeActQry)
+				{
+					
+					Plan *actplan = (Plan *)merge_action_planner(glob, 
+																		(Query *)lfirst(l),
+																		(Plan *)linitial(top_plan->plans)
+																	);
+
+					top_plan->mergeActPlan = lappend(top_plan->mergeActPlan, actplan);
+				}
+
+			}
 		}
 	}
 
@@ -584,6 +604,107 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	return plan;
 }
 
+
+
+ModifyTable *
+merge_action_planner(PlannerGlobal *glob, Query *parse,
+				 Plan *top_plan)
+{
+	PlannerInfo *root;
+	MergeAction	*actplan;
+	ModifyTable *result;
+	
+	List	   	*returningLists;
+	List 		*rowMarks;
+
+	/* Create a PlannerInfo data structure for this subquery */
+	root = makeNode(PlannerInfo);
+	root->parse = parse;
+	root->glob = glob;
+	root->query_level = 1;
+	root->parent_root = NULL;
+	root->planner_cxt = CurrentMemoryContext;
+	root->init_plans = NIL;
+	root->cte_plan_ids = NIL;
+	root->eq_classes = NIL;
+	root->append_rel_list = NIL;
+
+	root->hasRecursion = false;
+	root->wt_param_id = -1;
+	root->non_recursive_plan = NULL;
+
+
+	/*
+	 * no having clause in a merge action
+	 */
+	Assert(parse->havingQual == NULL);
+
+	/* Clear this flag; might get set in distribute_qual_to_rels */
+	root->hasPseudoConstantQuals = false;
+
+	/*
+	 * Do expression preprocessing on targetlist and quals.
+	 */
+
+	
+	parse->targetList = (List *)
+		preprocess_expression(root, (Node *) parse->targetList,
+							  EXPRKIND_TARGET);
+
+	preprocess_qual_conditions(root, (Node *) parse->jointree);
+
+	/*
+	 * Do the main planning.  If we have an inherited target relation, that
+	 * needs special processing, else go straight to grouping_planner.
+	 */
+
+
+	actplan = makeNode(MergeAction);
+	actplan->operation = parse->commandType;
+
+	/*copy the cost from the top_plan*/
+	actplan->plan.startup_cost = top_plan->startup_cost;
+	actplan->plan.total_cost = top_plan->total_cost;
+	actplan->plan.plan_rows = top_plan->plan_rows;
+	actplan->plan.plan_width = top_plan->plan_width;
+	
+	
+	actplan->plan.targetlist = preprocess_targetlist(root,parse->targetList);
+
+	actplan->plan.qual = (List *)parse->jointree->quals;
+	
+	if (parse->returningList)
+	{
+		List	   *rlist;
+
+		Assert(parse->resultRelation);
+		rlist = set_returning_clause_references(root->glob,
+												parse->returningList,
+												&actplan->plan,
+											  parse->resultRelation);
+		returningLists = list_make1(rlist);
+	}
+	else
+		returningLists = NIL;
+
+
+	if (parse->rowMarks)
+		rowMarks = NIL;
+	else
+		rowMarks = root->rowMarks;
+	
+	result = make_modifytable(parse->commandType,
+										   copyObject(root->resultRelations),
+											 list_make1(actplan),
+											 returningLists,
+											 rowMarks,
+											 SS_assign_special_param(root));
+
+	
+	return result;
+}
+
+
 /*
  * preprocess_expression
  *		Do subquery_planner's preprocessing work for an expression,
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
index 59d3518..5685d52 100644
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -78,13 +78,20 @@ preprocess_targetlist(PlannerInfo *root, List *tlist)
 								  result_relation, range_table);
 
 	/*
-	 * for "update" and "delete" queries, add ctid of the result relation into
+	 * for "update" , "delete"  and "merge" queries, add ctid of the result relation into
 	 * the target list so that the ctid will propagate through execution and
 	 * ExecutePlan() will be able to identify the right tuple to replace or
 	 * delete.	This extra field is marked "junk" so that it is not stored
 	 * back into the tuple.
+	 *  
+	 * BUT, if the query node is a merge action, we don't need to expend the ctid attribute in tlist.
+	 * The tlist of the merge top level plan already contains a "ctid" junk attr of the target relation.
 	 */
-	if (command_type == CMD_UPDATE || command_type == CMD_DELETE)
+	 
+	if(!parse->isMergeAction  &&  
+			(command_type == CMD_UPDATE || 
+			command_type == CMD_DELETE || 
+			command_type == CMD_MERGE))
 	{
 		TargetEntry *tle;
 		Var		   *var;
diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 6b99a10..89fe1e3 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -47,6 +47,8 @@ static Query *transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt);
 static Query *transformInsertStmt(ParseState *pstate, InsertStmt *stmt);
 static List *transformInsertRow(ParseState *pstate, List *exprlist,
 				   List *stmtcols, List *icolumns, List *attrnos);
+
+static Query *transformMergeStmt(ParseState *pstate, MergeStmt *stmt);
 static Query *transformSelectStmt(ParseState *pstate, SelectStmt *stmt);
 static Query *transformValuesClause(ParseState *pstate, SelectStmt *stmt);
 static Query *transformSetOperationStmt(ParseState *pstate, SelectStmt *stmt);
@@ -164,17 +166,24 @@ transformStmt(ParseState *pstate, Node *parseTree)
 			 * Optimizable statements
 			 */
 		case T_InsertStmt:
+		case T_MergeInsert:
 			result = transformInsertStmt(pstate, (InsertStmt *) parseTree);
 			break;
 
 		case T_DeleteStmt:
+		case T_MergeDelete:
 			result = transformDeleteStmt(pstate, (DeleteStmt *) parseTree);
 			break;
 
 		case T_UpdateStmt:
+		case T_MergeUpdate:
 			result = transformUpdateStmt(pstate, (UpdateStmt *) parseTree);
 			break;
 
+		case T_MergeStmt:
+			result = transformMergeStmt(pstate, (MergeStmt *)parseTree);
+			break; 
+
 		case T_SelectStmt:
 			{
 				SelectStmt *n = (SelectStmt *) parseTree;
@@ -282,22 +291,33 @@ transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt)
 
 	qry->commandType = CMD_DELETE;
 
-	/* set up range table with just the result rel */
-	qry->resultRelation = setTargetTable(pstate, stmt->relation,
-								  interpretInhOption(stmt->relation->inhOpt),
-										 true,
-										 ACL_DELETE);
-
 	qry->distinctClause = NIL;
 
+	if(IsA(stmt,MergeDelete))
+		qry->isMergeAction = true;
 	/*
-	 * The USING clause is non-standard SQL syntax, and is equivalent in
-	 * functionality to the FROM list that can be specified for UPDATE. The
-	 * USING keyword is used rather than FROM because FROM is already a
-	 * keyword in the DELETE syntax.
-	 */
-	transformFromClause(pstate, stmt->usingClause);
+	* The input stmt could be a MergeDelete node. 
+	* In this case, we don't need the process on range table.
+	*/
+	if(IsA(stmt, DeleteStmt))
+	{
+		/* set up range table with just the result rel */
+		qry->resultRelation = setTargetTable(pstate, stmt->relation,
+									  interpretInhOption(stmt->relation->inhOpt),
+											 true,
+											 ACL_DELETE);
+
+		
 
+		/*
+		 * The USING clause is non-standard SQL syntax, and is equivalent in
+		 * functionality to the FROM list that can be specified for UPDATE. The
+		 * USING keyword is used rather than FROM because FROM is already a
+		 * keyword in the DELETE syntax.
+		 */
+		transformFromClause(pstate, stmt->usingClause);
+	}
+	
 	qual = transformWhereClause(pstate, stmt->whereClause, "WHERE");
 
 	qry->returningList = transformReturningList(pstate, stmt->returningList);
@@ -342,11 +362,16 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 	qry->commandType = CMD_INSERT;
 	pstate->p_is_insert = true;
 
+	if(IsA(stmt,MergeInsert))
+		qry->isMergeAction = true;
+	
 	/*
 	 * We have three cases to deal with: DEFAULT VALUES (selectStmt == NULL),
 	 * VALUES list, or general SELECT input.  We special-case VALUES, both for
 	 * efficiency and so we can handle DEFAULT specifications.
 	 */
+
+	/*a MergeInsert statment is always a VALUE clause*/
 	isGeneralSelect = (selectStmt && selectStmt->valuesLists == NIL);
 
 	/*
@@ -382,7 +407,8 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 	 * mentioned in the SELECT part.  Note that the target table is not added
 	 * to the joinlist or namespace.
 	 */
-	qry->resultRelation = setTargetTable(pstate, stmt->relation,
+	if(IsA(stmt,InsertStmt))/*for MergeInsert, no need to do this*/ 
+		qry->resultRelation = setTargetTable(pstate, stmt->relation,
 										 false, false, ACL_INSERT);
 
 	/* Validate stmt->cols list, or build default list if no list given */
@@ -799,6 +825,7 @@ transformSelectStmt(ParseState *pstate, SelectStmt *stmt)
 	/* process the FROM clause */
 	transformFromClause(pstate, stmt->fromClause);
 
+
 	/* transform targetlist */
 	qry->targetList = transformTargetList(pstate, stmt->targetList);
 
@@ -1730,16 +1757,23 @@ transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt)
 	qry->commandType = CMD_UPDATE;
 	pstate->p_is_update = true;
 
-	qry->resultRelation = setTargetTable(pstate, stmt->relation,
-								  interpretInhOption(stmt->relation->inhOpt),
-										 true,
-										 ACL_UPDATE);
+	if(IsA(stmt,MergeUpdate))
+		qry->isMergeAction = true;
 
-	/*
-	 * the FROM clause is non-standard SQL syntax. We used to be able to do
-	 * this with REPLACE in POSTQUEL so we keep the feature.
-	 */
-	transformFromClause(pstate, stmt->fromClause);
+	
+	if(IsA(stmt, UpdateStmt))/*for MergeUpdate, no need to do this*/
+	{
+		qry->resultRelation = setTargetTable(pstate, stmt->relation,
+									  interpretInhOption(stmt->relation->inhOpt),
+											 true,
+											 ACL_UPDATE);
+
+		/*
+		 * the FROM clause is non-standard SQL syntax. We used to be able to do
+		 * this with REPLACE in POSTQUEL so we keep the feature.
+		 */
+		transformFromClause(pstate, stmt->fromClause);
+	}
 
 	qry->targetList = transformTargetList(pstate, stmt->targetList);
 
@@ -2241,3 +2275,336 @@ applyLockingClause(Query *qry, Index rtindex,
 	rc->pushedDown = pushedDown;
 	qry->rowMarks = lappend(qry->rowMarks, rc);
 }
+
+
+
+/*transform a action of merge command into a query. 
+No change of the pstate range table is allowed in this function. 
+*/
+static Query *
+transformMergeActions(ParseState *pstate, MergeStmt *stmt, MergeConditionAction *condact)
+{
+	Query *actqry = makeNode(Query);
+	A_Expr *match_expr; //the expr of matched/not matched
+	A_Expr *act_qual_expr;
+
+	/*firstly, we need to make sure that DELETE and UPDATE actions are only taken in MATCHED condition 
+	and INSERTs are only takend when not MATCHED
+	*/
+	if(IsA(condact->action, MergeDelete)) 
+	{	
+		if(!condact->match) 
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+		 		errmsg("The DELETE action in MERGE command is not allowed when NOT MATCHED")));
+	}
+	else if(IsA(condact->action, MergeUpdate))
+	{	
+		if(!condact->match) 
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+		 		errmsg("The UPDATE action in MERGE command is not allowed when NOT MATCHED")));
+	}
+	else if(IsA(condact->action, MergeInsert))
+	{	
+		if(condact->match) 
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+		 		errmsg("The INSERT action in MERGE command is not allowed when MATCHED")));
+	}
+	else
+		ereport(ERROR,
+			(errcode(ERRCODE_SYNTAX_ERROR),
+			 errmsg("UNKONWN action type in MERGE")));
+
+
+		
+	/*combine the condtion of this act with the ON qual of the merge command
+	do a copy of the merge condtion for safety. 
+	*/
+
+	/*
+	if(condact->match) 
+		match_expr = copyObject(stmt->matchCondition);
+	else
+		match_expr = makeA_Expr(AEXPR_NOT, NIL, NULL, 
+									copyObject(stmt->matchCondition), 1);
+											
+
+	if(condact->condition)
+		act_qual_expr = makeA_Expr(AEXPR_AND, NIL, condact->condition, (Node *)match_expr, 2);
+	else
+		act_qual_expr = match_expr;
+
+	*/
+
+	act_qual_expr = condact->condition;
+	
+	/*use the transfomStmt() to parse all types of actions*/
+	if(IsA(condact->action, MergeDelete))
+	{
+		/*a delete action*/
+		MergeDelete *deleteact = (MergeDelete *)(condact->action);
+		Assert(IsA(deleteact,DeleteStmt));
+		
+		deleteact->relation = stmt->relation;
+		deleteact->usingClause = stmt->source;
+		deleteact->whereClause = (Node *)act_qual_expr;
+
+		/*parse the action query*/
+		actqry = transformStmt(pstate, (Node *)deleteact);
+
+		if(!IsA(actqry, Query) || actqry->commandType != CMD_DELETE || actqry->utilityStmt != NULL)
+			elog(ERROR, "improper DELETE action in merge stmt");
+
+		return actqry;
+	}
+	else if(IsA(condact->action, MergeUpdate))
+	{
+		/*an update action*/
+		MergeUpdate *updateact = (MergeUpdate *)(condact->action);
+
+		/*the "targetlist" of the updateact is filled in the parser */
+		updateact->relation = stmt->relation;
+		updateact->fromClause = stmt->source;
+		updateact->whereClause = (Node *)act_qual_expr;
+
+		/*parse the action query*/
+		actqry = transformStmt(pstate, (Node *)updateact);
+
+		if(!IsA(actqry, Query) || actqry->commandType != CMD_UPDATE|| actqry->utilityStmt != NULL)
+			elog(ERROR, "improper UPDATE action in merge stmt");
+
+		return actqry;
+	}
+	else if(IsA(condact->action, MergeInsert))
+	{
+		/*an insert action*/
+		Node *qual;
+		MergeInsert *insertact;
+
+		insertact = (MergeInsert *)(condact->action);
+		
+		
+		/*the "cols" and "selectStmt" of the insertact is filled in the parser */
+		insertact->relation = stmt->relation;
+
+		/*
+		the merge insert action has a strange feature. 
+		In an ordinary INSERT, the VALUES list can only contains constants and DEFAULT. (am I right??)
+		But in the INSERT action of MERGE command, the VALUES list can have expressions with variables(attributes of the targe and source tables).
+		Besides, in the ordinary INSERT, a VALUES list can never be followed by a WHERE clause. But in MERGE INSERT action, there are matching conditions. 
+
+		Thus, the output qry of this function is an INSERT query in the style of "INSERT...VALUES...", except that we have other range tables and a WHERE clause.
+		Note that it is also different from the "INSERT ... SELECT..." query, in which the whole SELECT is a subquery. (We don't have subquery here).
+		We construct this novel query structure in order to keep consitency with other merge action types (DELETE, UPDATE). 
+		In this way, all the merge action queries are in fact share the very same Range Table, They only differs in their target lists and join trees
+		
+		*/
+		
+				
+		/*parse the action query, this will call transformInsertStmt() which analyzes the VALUES list.*/
+		actqry = transformStmt(pstate, (Node *)insertact);
+
+		/*do the WHERE clause here, Since the transformInsertStmt() function only analyzes the VALUES list but not the WHERE clause*/
+		qual = transformWhereClause(pstate,(Node *)act_qual_expr, "WHERE");
+		
+		actqry->jointree = makeFromExpr(pstate->p_joinlist, qual);
+
+		
+		if(!IsA(actqry, Query) || actqry->commandType != CMD_INSERT|| actqry->utilityStmt != NULL)
+			elog(ERROR, "improper INSERT action in merge stmt");
+
+
+		return actqry;
+	}
+	else
+		elog(ERROR, "unknown action type in MERGE");
+
+	/*never comes here*/
+	return NULL;
+}
+
+
+
+static Query *
+transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
+{
+	Query	   *qry; 
+
+	ColumnRef *starRef;
+	ResTarget *starResTarget;
+	ListCell *act;
+	ListCell *l;
+	JoinExpr *joinexp;
+	int 	rtindex;
+
+	/*this will never happen, since the garm.y is restricted that only one rel name is allowed to appear in the source table position. 
+	However, if we extent the command in future, we may need to note this check here. 
+	*/
+	if(list_length(stmt->source) != 1) 
+		ereport(ERROR,
+			(errcode(ERRCODE_SYNTAX_ERROR),
+			 errmsg("now we only accept merge command with only ONE source table")));
+		
+	/*now, do the real tranformation of the merge command. */
+	qry = makeNode(Query);
+	qry->commandType = CMD_MERGE;
+
+	/*
+	What we are doing here is to create a query like 
+		"SELECT * FROM <source_rel> LEFT JOIN <target_rel> ON <match_condition>;"
+	Note:	
+	1. we set the "match condition" as the join qualification. 
+	The left join will scan both the matched and non-matched tuples.
+
+	2. a normal SELECT query has no "target relation". 
+	But here we need to set the targe relation in query, like the UPDATE/DELETE/INSERT queries. 
+	So this is a left join SELECT with a "target table" in its range table. 
+
+	3. We don't have a specific ACL level for Merge, here we just use ACL_SELECT. 
+	But we will add other ACL levels when handle each merge actions.  
+	*/
+
+
+	/*before analyze the FROM clause, we need to set the target table. 
+	We cannot call setTargetTable() function directly. 
+	We only need the lock target relation, without adding it to Range table. 
+	*/
+	
+	
+	setTargetTableLock(pstate, stmt->relation);
+	
+	
+	
+	/*create the FROM clause. Make the join expression first*/
+	joinexp = makeNode(JoinExpr);
+	joinexp->jointype = JOIN_LEFT;
+	joinexp->isNatural = FALSE;
+	joinexp->larg = linitial(stmt->source);/*source list has only one element*/
+	joinexp->rarg = (Node *)stmt->relation;
+	joinexp->quals = stmt->matchCondition; /*match condtion*/
+
+	/*transform the FROM clause. The target relation and source relation will be add to Rtable here.	*/
+	transformFromClause(pstate, list_make1(joinexp));
+
+	/*the targetList of the main query is "*"	  
+	*/
+	starRef = makeNode(ColumnRef);	
+	starRef->fields = list_make1(makeNode(A_Star));					
+	starRef->location = 1;					
+
+	starResTarget = makeNode(ResTarget);					
+	starResTarget->name = NULL;					
+	starResTarget->indirection = NIL;					
+	starResTarget->val = (Node *)starRef;					
+	starResTarget->location = 1;
+	
+	qry->targetList = transformTargetList(pstate, list_make1(starResTarget));
+
+	/*we don't need the WHERE clause here. Set it null. */
+	qry->jointree = makeFromExpr(pstate->p_joinlist, NULL);
+
+	/*now , we find out the RTE for the target relation, and do some unfinished jobs*/
+	rtindex = 1;
+	foreach(l, pstate->p_rtable)
+	{
+		RangeTblEntry *rte = (RangeTblEntry *)lfirst(l);
+		if(rte->relid == pstate->p_target_relation->rd_id) /*find the RTE*/
+		{
+			pstate->p_target_rangetblentry = rte;
+			rte->requiredPerms = ACL_SELECT;	
+			qry->resultRelation = rtindex;
+			break;
+		}
+		rtindex++;
+	}
+
+	if(pstate->p_target_rangetblentry == NULL)
+		elog(ERROR, "cannot find the RTE for target table");
+	
+
+	qry->rtable = pstate->p_rtable;
+
+	qry->hasSubLinks = pstate->p_hasSubLinks;
+
+	/*
+	 * Top-level aggregates are simply disallowed in MERGE
+	 */
+	if (pstate->p_hasAggs)
+		ereport(ERROR,
+				(errcode(ERRCODE_GROUPING_ERROR),
+				 errmsg("cannot use aggregate function in top level of MERGE"),
+				 parser_errposition(pstate,
+									locate_agg_of_level((Node *) qry, 0))));
+	if (pstate->p_hasWindowFuncs)
+		ereport(ERROR,
+				(errcode(ERRCODE_WINDOWING_ERROR),
+				 errmsg("cannot use window function in MERGE"),
+				 parser_errposition(pstate,
+									locate_windowfunc((Node *) qry))));
+
+
+
+
+	/*
+		the main query is done.
+	then for each actions ,we transform it to a seperate query.
+	the action queries shares the exactly same range table with the main query. 
+	in other words, in the extra condtions of the sub actions, we don't allow involvement of new tables
+	*/
+	
+	qry->mergeActQry = NIL;
+
+	foreach(act,stmt->actions)
+	{
+		MergeConditionAction *mca = lfirst(act);
+		Query *actqry;
+
+		switch(mca->action->type)
+		{
+			case T_MergeDelete:
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_DELETE;
+				break;
+			case T_MergeUpdate:
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_UPDATE;
+				break;
+			case T_MergeInsert:
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_INSERT;				
+				break;
+			default:
+				elog(ERROR, "unknown MERGE action type %d", mca->type);
+				break;
+
+		}
+
+
+		/*transform the act (and its condition) as a single query. Link it to the top-level query*/
+		actqry = transformMergeActions(pstate, stmt, mca);
+
+		/*since we don't invoke setTargetTable() in transformMergeActions(), we need to set actqry->resultRelation here
+		*/
+		actqry->resultRelation = qry->resultRelation;
+
+
+		qry->mergeActQry = lappend(qry->mergeActQry, actqry);
+	}
+
+
+	/*for a single-action merge, we just stransform it into a orignial update/delete command.
+	but the insert action cannot take this shortcut.
+	*/
+	/*
+	if(list_length(stmt->actions) == 1)
+	{
+		Query *q = linitial(qry->mergeActQry);
+		if(q->commandType == CMD_DELETE || q->commandType == CMD_UPDATE)
+			return q;
+	}
+	*/
+	return qry;
+
+	
+}
+
+
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 3f6eeeb..c139bd7 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -212,6 +212,12 @@ static TypeName *TableFuncTypeName(List *columns);
 		DropOwnedStmt ReassignOwnedStmt
 		AlterTSConfigurationStmt AlterTSDictionaryStmt
 
+%type <node>	MergeStmt  opt_and_condition  merge_condition_action   merge_action
+%type <boolean> opt_not	
+%type <list> 	merge_condition_action_list
+
+
+
 %type <node>	select_no_parens select_with_parens select_clause
 				simple_select values_clause
 
@@ -233,7 +239,8 @@ static TypeName *TableFuncTypeName(List *columns);
 %type <boolean>	opt_force opt_or_replace
 				opt_grant_grant_option opt_grant_admin_option
 				opt_nowait opt_if_exists opt_with_data
-
+				
+				
 %type <list>	OptRoleList AlterOptRoleList
 %type <defelt>	CreateOptRoleElem AlterOptRoleElem
 
@@ -504,6 +511,8 @@ static TypeName *TableFuncTypeName(List *columns);
 
 	MAPPING MATCH MAXVALUE MINUTE_P MINVALUE MODE MONTH_P MOVE
 
+	MATCHED MERGE
+	
 	NAME_P NAMES NATIONAL NATURAL NCHAR NEXT NO NOCREATEDB
 	NOCREATEROLE NOCREATEUSER NOINHERIT NOLOGIN_P NONE NOSUPERUSER
 	NOT NOTHING NOTIFY NOTNULL NOWAIT NULL_P NULLIF NULLS_P NUMERIC
@@ -725,6 +734,7 @@ stmt :
 			| ListenStmt
 			| LoadStmt
 			| LockStmt
+			| MergeStmt 
 			| NotifyStmt
 			| PrepareStmt
 			| ReassignOwnedStmt
@@ -7297,6 +7307,101 @@ set_target_list:
 /*****************************************************************************
  *
  *		QUERY:
+ *				MERGE STATEMENT
+ *
+ *****************************************************************************/
+
+
+MergeStmt: 
+			MERGE INTO relation_expr_opt_alias
+			USING  table_ref
+			ON a_expr
+			merge_condition_action_list
+				{
+					MergeStmt *m = makeNode(MergeStmt);
+
+					m->relation = $3;
+					m->source = list_make1($5);  /*although we have only one USING table, but we still make it a list, maybe in future we will allow mutliple USING tables.*/
+					m->matchCondition = $7;
+					m->actions = $8;
+
+					$$ = (Node *)m;
+				}
+				;
+	
+merge_condition_action_list: 
+							merge_condition_action 		
+								{ $$ = list_make1($1); }
+							| merge_condition_action_list merge_condition_action   
+								{ $$ = lappend($1,$2); }
+							;	
+
+merge_condition_action: 	
+							WHEN opt_not MATCHED opt_and_condition THEN merge_action
+							{
+								MergeConditionAction *m = makeNode(MergeConditionAction);
+
+								m->match = $2;
+								m->condition = $4;
+								m->action = $6;
+
+								$$ = (Node *)m;
+							}
+							;
+
+
+opt_and_condition:	
+					AND a_expr 		{$$ = $2;}
+					| /*EMPTY*/ 		{$$ = NULL;}
+					;
+
+opt_not:	
+			NOT			{$$ = false;}
+			| /*EMPTY*/	{$$ = true;}
+			;
+
+merge_action: 	
+				DELETE_P	
+					{$$ = (Node *)makeNode(MergeDelete);}
+				| UPDATE SET set_clause_list 
+					{
+						UpdateStmt *n = makeNode(MergeUpdate);
+						n->targetList = $3;
+						$$ = (Node *)n;
+					}
+				| INSERT values_clause
+					{
+						InsertStmt *n = makeNode(MergeInsert);
+						n->cols = NIL;
+						n->selectStmt = $2;
+
+						$$ = (Node *)n;
+					}
+					
+				| INSERT '(' insert_column_list ')' values_clause
+					{
+						InsertStmt *n = makeNode(MergeInsert);
+						n->cols = $3;
+						n->selectStmt = $5;
+
+						$$ = (Node *)n;
+					}
+				| INSERT DEFAULT VALUES
+					{
+						InsertStmt *n = makeNode(MergeInsert);
+						n->cols = NIL;
+						n->selectStmt = NULL;
+
+						$$ = (Node *)n; 
+					}
+					
+				;	
+				
+
+
+/*****************************************************************************
+ *
+ *		QUERY:
  *				CURSOR STATEMENTS
  *
  *****************************************************************************/
@@ -10935,7 +11040,9 @@ unreserved_keyword:
 			| LOGIN_P
 			| MAPPING
 			| MATCH
+			| MATCHED
 			| MAXVALUE
+			| MERGE
 			| MINUTE_P
 			| MINVALUE
 			| MODE
diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index f30132a..657dd9c 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -213,6 +213,29 @@ setTargetTable(ParseState *pstate, RangeVar *relation,
 	return rtindex;
 }
 
+
+void
+setTargetTableLock(ParseState *pstate, RangeVar *relation)
+{
+	
+	/* Close old target; this could only happen for multi-action rules */
+	if (pstate->p_target_relation != NULL)
+		heap_close(pstate->p_target_relation, NoLock);
+
+	/*
+	 * Open target rel and grab suitable lock (which we will hold till end of
+	 * transaction).
+	 *
+	 * free_parsestate() will eventually do the corresponding heap_close(),
+	 * but *not* release the lock.
+	 */
+	pstate->p_target_relation = parserOpenTable(pstate, relation,
+												RowExclusiveLock);
+
+	
+}
+
+
 /*
  * Simplify InhOption (yes/no/default) into boolean yes/no.
  *
diff --git a/src/backend/rewrite/rewriteHandler.c b/src/backend/rewrite/rewriteHandler.c
index 25b44dd..287fa1f 100644
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -1837,6 +1837,45 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 }
 
 
+#define insert_rewrite (1<<0) /*insert merge action has already been processed by rewriter*/
+#define delete_rewrite (1<<1) 
+#define update_rewrite (1<<2)
+
+#define	insert_instead (1<<3) /*insert merge action is fully replace by rules.*/
+#define delete_instead (1<<4)
+#define update_instead (1<<5)
+
+
+#define merge_action_already_rewrite(acttype, flag) \
+	((acttype == CMD_INSERT && (flag & insert_rewrite)) || \
+		(acttype == CMD_UPDATE && (flag & update_rewrite)) || \
+		(acttype == CMD_DELETE && (flag & delete_rewrite)))
+
+
+#define set_action_rewrite(acttype, flag)	\
+				if(acttype == CMD_INSERT)  \
+					{flag |= insert_rewrite;}\
+				else if(acttype == CMD_UPDATE)  \
+					{flag |= update_rewrite;}\
+				else if(acttype == CMD_DELETE)  \
+					{flag |= delete_rewrite;}
+
+
+				
+#define merge_action_instead(acttype, flag)		\
+			((acttype == CMD_INSERT && (flag & insert_instead)) || \
+				(acttype == CMD_UPDATE && (flag & update_instead)) || \
+				(acttype == CMD_DELETE && (flag & delete_instead)))
+
+#define set_action_instead(acttype, flag)\
+				if(acttype == CMD_INSERT)  \
+					{flag |= insert_instead;}\
+				else if(acttype == CMD_UPDATE)  \
+					{flag |= update_instead;}\
+				else if(acttype == CMD_DELETE)  \
+					{flag |= delete_instead;}
+
+
 /*
  * QueryRewrite -
  *	  Primary entry point to the query rewriter.
@@ -1861,7 +1900,133 @@ QueryRewrite(Query *parsetree)
 	 *
 	 * Apply all non-SELECT rules possibly getting 0 or many queries
 	 */
-	querylist = RewriteQuery(parsetree, NIL);
+
+	
+	if(parsetree->commandType == CMD_MERGE)
+	{
+		/*for merge query, we have a set of lower-level action queries (not subquery).
+		//each of these action queries should be applied to RewriteQuery(). 
+		*/
+		ListCell   *cell,
+				   *prev,
+				   *next;
+
+		int flag = 0;
+
+		
+		List *pre_qry = NIL;
+		List *post_qry = NIL;
+
+
+		querylist = NIL;
+		
+
+		/*rewrite the merge action queries one by one.*/
+		prev = NULL;
+
+		for (cell = list_head(parsetree->mergeActQry); cell; cell = next)
+		{
+			List *queryList4action = NIL;
+			Query *actionqry;
+			Query *q;
+
+			
+			actionqry = lfirst(cell);
+
+			next = lnext(cell);
+
+			/*if this kind of actions are fully replaced by rules, we delete it from the action list*/	
+			if(merge_action_instead(actionqry->commandType, flag))
+			{
+				parsetree->mergeActQry = list_delete_cell(parsetree->mergeActQry, cell, prev);
+				continue;
+			}
+
+
+			/*if this kind of actions are already processed by rewriter, skip it.*/
+			if(merge_action_already_rewrite(actionqry->commandType, flag))
+			{
+
+			
+				prev = cell; 
+				continue;
+			}
+
+			/*ok this action has not been processed before, let's do it now.*/
+			
+			queryList4action = RewriteQuery(actionqry, NIL);
+			set_action_rewrite(actionqry->commandType,flag); /*this kind of actions has been processed.*/
+
+			/*if the returning list is nil, this merge action is replaced by a do-nothing rule*/
+			if(queryList4action == NIL) 
+			{
+				/*set the flag for other merge actions of the same type*/
+				set_action_instead(actionqry->commandType, flag);
+				/*delete the action.*/
+				parsetree->mergeActQry = list_delete_cell(parsetree->mergeActQry, cell, prev);
+				continue;
+			}
+
+			
+			/*the merge action query could be one of the elements in the rewriten list. 
+			//if it is in the list, it must be the head or tail.
+			*/
+			q = (Query *)linitial(queryList4action);
+			if(q->querySource == QSRC_ORIGINAL)
+			{
+				/*the merge action is the head, the remaining part of the list are the queries generated by rules
+				//we put them in the post_qry list. 
+				*/
+				if(querylist == NIL)
+					querylist = list_make1(parsetree);
+
+
+				queryList4action = list_delete_first(queryList4action);
+				post_qry = list_concat(post_qry,queryList4action);
+				prev = cell; 
+				continue;
+
+			}
+			
+			
+			q = (Query *)llast(queryList4action);
+			if(q->querySource == QSRC_ORIGINAL)
+			{
+				/*the merge action is the tail. Put the rule queries in pre_qry list*/
+
+				if(querylist == NIL)
+					querylist = list_make1(parsetree);
+					
+				queryList4action = list_truncate(queryList4action,list_length(queryList4action)-1);
+
+				pre_qry = list_concat(pre_qry,queryList4action);
+
+				prev = cell; 
+				continue;
+
+			}	
+				
+
+			/*here, the merge action query is not in the rewriten query list, which means the action should be deleted
+			//It is replaced by INSTEAD rule(s). We need to delete the action  
+			*/
+			post_qry = list_concat(post_qry,queryList4action);	
+			set_action_instead(actionqry->commandType, flag);
+			parsetree->mergeActQry = list_delete_cell(parsetree->mergeActQry, cell, prev);
+		}				
+
+		
+
+		/*finally, put the 3 lists into one. 
+		If all the merge actions are replaced by rules, the original merge query 
+		will not be involved in the querylist.
+		*/
+		querylist = list_concat(pre_qry,querylist);
+		querylist = list_concat(querylist, post_qry);
+			
+	}
+	else
+		querylist = RewriteQuery(parsetree, NIL);
 
 	/*
 	 * Step 2
diff --git a/src/backend/tcop/pquery.c b/src/backend/tcop/pquery.c
index 8ad4915..0dc3117 100644
--- a/src/backend/tcop/pquery.c
+++ b/src/backend/tcop/pquery.c
@@ -225,6 +225,10 @@ ProcessQuery(PlannedStmt *plan,
 				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
 						 "DELETE %u", queryDesc->estate->es_processed);
 				break;
+			case CMD_MERGE:
+				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
+						 "MERGE %u", queryDesc->estate->es_processed);
+				break;
 			default:
 				strcpy(completionTag, "???");
 				break;
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 8960246..2733e5d 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -125,6 +125,7 @@ CommandIsReadOnly(Node *parsetree)
 			case CMD_UPDATE:
 			case CMD_INSERT:
 			case CMD_DELETE:
+			case CMD_MERGE:
 				return false;
 			default:
 				elog(WARNING, "unrecognized commandType: %d",
@@ -1398,6 +1399,10 @@ CreateCommandTag(Node *parsetree)
 			tag = "SELECT";
 			break;
 
+		case T_MergeStmt:
+			tag = "MERGE";
+			break;
+		
 			/* utility statements --- same whether raw or cooked */
 		case T_TransactionStmt:
 			{
@@ -2235,6 +2240,7 @@ GetCommandLogLevel(Node *parsetree)
 		case T_InsertStmt:
 		case T_DeleteStmt:
 		case T_UpdateStmt:
+		case T_MergeStmt:
 			lev = LOGSTMT_MOD;
 			break;
 
diff --git a/src/include/executor/nodeModifyTable.h b/src/include/executor/nodeModifyTable.h
index 67ba3e8..7ae2f0a 100644
--- a/src/include/executor/nodeModifyTable.h
+++ b/src/include/executor/nodeModifyTable.h
@@ -16,6 +16,9 @@
 #include "nodes/execnodes.h"
 
 extern ModifyTableState *ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags);
+
+extern PlanState *ExecInitMergeAction(MergeAction *node, EState *estate, int eflags);
+
 extern TupleTableSlot *ExecModifyTable(ModifyTableState *node);
 extern void ExecEndModifyTable(ModifyTableState *node);
 extern void ExecReScanModifyTable(ModifyTableState *node);
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 09fdb5d..6c0ae0c 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1031,6 +1031,7 @@ typedef struct ModifyTableState
 	int			mt_whichplan;	/* which one is being executed (0..n-1) */
 	EPQState	mt_epqstate;	/* for evaluating EvalPlanQual rechecks */
 	bool		fireBSTriggers; /* do we need to fire stmt triggers? */
+	List 		*mergeActPstates; /*the list of the planstate of each meger command action. NIL if this is not a merge command, all actions' */
 } ModifyTableState;
 
 /* ----------------
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index a5f5df5..15d11a0 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -44,6 +44,7 @@ typedef enum NodeTag
 	T_Plan = 100,
 	T_Result,
 	T_ModifyTable,
+	T_MergeAction,
 	T_Append,
 	T_RecursiveUnion,
 	T_BitmapAnd,
@@ -261,6 +262,15 @@ typedef enum NodeTag
 	T_DeleteStmt,
 	T_UpdateStmt,
 	T_SelectStmt,
+
+	
+	T_MergeStmt,
+	T_MergeConditionAction,
+	T_MergeUpdate, 
+	T_MergeDelete,  
+	T_MergeInsert,
+
+	
 	T_AlterTableStmt,
 	T_AlterTableCmd,
 	T_AlterDomainStmt,
@@ -511,6 +521,7 @@ typedef enum CmdType
 	CMD_UPDATE,					/* update stmt */
 	CMD_INSERT,					/* insert stmt */
 	CMD_DELETE,
+	CMD_MERGE,						/*merge stmt*/
 	CMD_UTILITY,				/* cmds like create, destroy, copy, vacuum,
 								 * etc. */
 	CMD_NOTHING					/* dummy command for instead nothing rules
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index b591073..d6de83c 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -146,6 +146,11 @@ typedef struct Query
 
 	Node	   *setOperations;	/* set-operation tree if this is top level of
 								 * a UNION/INTERSECT/EXCEPT query */
+
+	bool		 isMergeAction; /*if this query is a merge action. */	 
+
+	List 		*mergeActQry; /* the list of all the merge actions. 
+								* used only for merge query statment*/							 
 } Query;
 
 
@@ -990,6 +995,30 @@ typedef struct SelectStmt
 	/* Eventually add fields for CORRESPONDING spec here */
 } SelectStmt;
 
+/*ZBX: the structure for MERGE command statement*/
+typedef struct MergeStmt
+{
+	NodeTag		type;
+	RangeVar   	*relation;		/*targe relation for merge */
+	List		*source;		/* source relations for the merge. Currently, we only allwo single-source merge, so the length of this list should always be 1 */
+	Node	   	*matchCondition;	/* qualifications of the merge*/
+	List	   	*actions;		/*list  of MergeConditionAction structure. It stores all the match / non-matching conditions and the corresponding actions*/
+
+}MergeStmt;
+
+/*the structure for the actions of MERGE command. Holds info of the clauses like "... WHEN MATCHED AND ... THEN UPDATE/DELETE/INSERT"
+*/
+typedef struct MergeConditionAction
+{
+	NodeTag		type;
+	bool 		match; /*match or not match*/
+	Node		*condition;/*the AND condition for this action*/
+	Node 		*action; /*the actions: delete , insert or update*/
+}MergeConditionAction;
+
+typedef UpdateStmt MergeUpdate;
+typedef DeleteStmt MergeDelete;
+typedef InsertStmt MergeInsert;
 
 /* ----------------------
  *		Set Operation node for post-analysis query trees
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 037bc0b..5c1bc5f 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -169,8 +169,16 @@ typedef struct ModifyTable
 	List	   *returningLists; /* per-target-table RETURNING tlists */
 	List	   *rowMarks;		/* PlanRowMarks (non-locking only) */
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
+	List 		*mergeActPlan;	/*the plans for merge actions, which are also ModifyTable nodes*/
 } ModifyTable;
 
+
+typedef struct MergeAction
+{
+	Plan plan;
+	CmdType	operation;/* INSERT, UPDATE, or DELETE */
+}MergeAction;
+
 /* ----------------
  *	 Append node -
  *		Generate the concatenation of the results of sub-plans.
diff --git a/src/include/optimizer/planner.h b/src/include/optimizer/planner.h
index 805dee7..6d7ff4f 100644
--- a/src/include/optimizer/planner.h
+++ b/src/include/optimizer/planner.h
@@ -34,6 +34,7 @@ extern Plan *subquery_planner(PlannerGlobal *glob, Query *parse,
 				 PlannerInfo *parent_root,
 				 bool hasRecursion, double tuple_fraction,
 				 PlannerInfo **subroot);
+extern ModifyTable *merge_action_planner(PlannerGlobal *glob, Query *parse, Plan *top_plan);
 
 extern Expr *expression_planner(Expr *expr);
 
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 49d4b6c..436d459 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -229,7 +229,9 @@ PG_KEYWORD("lock", LOCK_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("login", LOGIN_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("mapping", MAPPING, UNRESERVED_KEYWORD)
 PG_KEYWORD("match", MATCH, UNRESERVED_KEYWORD)
+PG_KEYWORD("matched", MATCHED, UNRESERVED_KEYWORD)
 PG_KEYWORD("maxvalue", MAXVALUE, UNRESERVED_KEYWORD)
+PG_KEYWORD("merge", MERGE, UNRESERVED_KEYWORD)
 PG_KEYWORD("minute", MINUTE_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("minvalue", MINVALUE, UNRESERVED_KEYWORD)
 PG_KEYWORD("mode", MODE, UNRESERVED_KEYWORD)
diff --git a/src/include/parser/parse_clause.h b/src/include/parser/parse_clause.h
index f3d3ee9..e4312d8 100644
--- a/src/include/parser/parse_clause.h
+++ b/src/include/parser/parse_clause.h
@@ -19,6 +19,8 @@
 extern void transformFromClause(ParseState *pstate, List *frmList);
 extern int setTargetTable(ParseState *pstate, RangeVar *relation,
 			   bool inh, bool alsoSource, AclMode requiredPerms);
+extern void setTargetTableLock(ParseState *pstate, RangeVar *relation);
+
 extern bool interpretInhOption(InhOption inhOpt);
 extern bool interpretOidsOption(List *defList);
 

tested_merge.patch0000644000076400010400000017043311426077071015631 0ustar  bxzhaiAdministratorsdiff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index b776ad1..cdb492b 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -73,6 +73,8 @@ static void show_sort_keys(SortState *sortstate, List *ancestors,
 static void show_sort_info(SortState *sortstate, ExplainState *es);
 static void show_hash_info(HashState *hashstate, ExplainState *es);
 static const char *explain_get_index_name(Oid indexId);
+static void ExplainMergeActions(ModifyTableState *mt_planstate, 
+									List *ancestors, ExplainState *es);
 static void ExplainScanTarget(Scan *plan, ExplainState *es);
 static void ExplainMemberNodes(List *plans, PlanState **planstates,
 				   List *ancestors, ExplainState *es);
@@ -636,6 +638,9 @@ ExplainNode(PlanState *planstate, List *ancestors,
 				case CMD_DELETE:
 					pname = operation = "Delete";
 					break;
+				case CMD_MERGE:
+					pname = operation = "Merge";
+					break;
 				default:
 					pname = "???";
 					break;
@@ -1190,6 +1195,8 @@ ExplainNode(PlanState *planstate, List *ancestors,
 	switch (nodeTag(plan))
 	{
 		case T_ModifyTable:
+			ExplainMergeActions((ModifyTableState *)planstate, ancestors, es);
+			
 			ExplainMemberNodes(((ModifyTable *) plan)->plans,
 							   ((ModifyTableState *) planstate)->mt_plans,
 							   ancestors, es);
@@ -1482,6 +1489,55 @@ explain_get_index_name(Oid indexId)
 	return result;
 }
 
+static void
+ExplainMergeActions(ModifyTableState *mt_planstate, List *ancestors, ExplainState *es)
+{
+	ListCell *l;
+	
+	if(mt_planstate->operation != CMD_MERGE || mt_planstate->mergeActPstates == NIL)
+		return;
+
+	foreach(l,mt_planstate->mergeActPstates)
+	{
+		ModifyTableState *mt_state = (ModifyTableState *)lfirst(l);
+
+		MergeActionState *act_pstate = (MergeActionState *)mt_state->mt_plans[0];
+
+		MergeAction *act_plan = (MergeAction *)act_pstate->ps.plan;
+
+		switch(act_pstate->operation)
+		{
+			case CMD_INSERT:
+				if(act_plan->flattenedqual)
+					ExplainPropertyText("Action", "Insert When Not Matched And",es);
+				else
+					ExplainPropertyText("Action", "Insert When Not Matched",es);				
+				break;
+			case CMD_UPDATE:
+				if(act_plan->flattenedqual)
+					ExplainPropertyText("Action", "Update When Matched And",es);
+				else
+					ExplainPropertyText("Action", "Update When Matched",es);	
+				break;
+			case CMD_DELETE:
+				if(act_plan->flattenedqual)
+					ExplainPropertyText("Action", "Delete When Matched And",es);
+				else
+					ExplainPropertyText("Action", "Delete When Matched",es);	
+				break;	
+			default:
+				elog(ERROR, "unknown merge action type");
+		}
+
+		/*
+		*	We need a faltened qual expression for show_qual
+		*/
+		show_qual(act_plan->flattenedqual, "  qual", &act_pstate->ps, ancestors, true, es);
+	}
+	
+}
+
+
 /*
  * Show the target of a Scan node
  */
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 2f33fdb..56c13ee 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -171,6 +171,7 @@ standard_ExecutorStart(QueryDesc *queryDesc, int eflags)
 		case CMD_INSERT:
 		case CMD_DELETE:
 		case CMD_UPDATE:
+		case CMD_MERGE:	
 			estate->es_output_cid = GetCurrentCommandId(true);
 			break;
 
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index f4cc7d9..2d1a4e7 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -153,6 +153,11 @@ ExecInitNode(Plan *node, EState *estate, int eflags)
 													   estate, eflags);
 			break;
 
+		case T_MergeAction:
+			result = (PlanState *) ExecInitMergeAction((MergeAction*) node,
+													   estate, eflags);
+			break;
+			
 		case T_Append:
 			result = (PlanState *) ExecInitAppend((Append *) node,
 												  estate, eflags);
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 8619ce3..bd84784 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -583,6 +583,116 @@ lreplace:;
 }
 
 
+static TupleTableSlot *
+ExecMerge(ItemPointer tupleid,
+		   TupleTableSlot *slot,
+		   TupleTableSlot *planSlot,
+		   ModifyTableState *node,
+		   EState *estate)
+{
+
+	TupleTableSlot *actslot = NULL;
+	TupleTableSlot *res = NULL;
+	ListCell *each;
+
+	/*
+	*	try the merge actions one by one
+	*/
+	foreach(each, node->mergeActPstates)
+	{
+		ModifyTableState *mt_pstate;
+
+		MergeActionState *action_pstate; 
+
+		ExprContext *econtext;
+
+		
+		mt_pstate = (ModifyTableState *)lfirst(each);
+
+		/*
+		*	mt_pstate is supposed to have only ONE mt_plans, 
+		*	which is a MergeActionState
+		*/
+		Assert(mt_pstate->mt_nplans == 1);
+
+		action_pstate = (MergeActionState *)mt_pstate->mt_plans[0];
+
+		/*
+		*	If tupleid == NULL, it is a NOT MATCHED case, in which we can only do INSERT action
+		*	If tupleid != NULL, it is a MATCHED case, in which we can only do UPDATE or DELETE action
+		*/		
+		if((tupleid == NULL && action_pstate->operation != CMD_INSERT) ||
+			(tupleid != NULL && action_pstate->operation == CMD_INSERT))
+		{
+			continue;
+		}
+
+		/*
+		*	Setup the expression context
+		*/
+		econtext = action_pstate->ps.ps_ExprContext;
+
+		/*
+		If the action has an additional qual, which is not satisfied, skip it
+		*/	
+		
+		if(action_pstate->ps.qual) 
+		{	
+			ResetExprContext(econtext);
+		
+			econtext->ecxt_scantuple = slot;
+			econtext->ecxt_outertuple = planSlot;
+
+			if(!ExecQual(action_pstate->ps.qual, econtext,false))
+			{	
+				continue;
+			}
+		}
+		/*
+		*	Now we start to exec this action. Firstly , project the result tuple slot. 
+		*	The merge action result slot is projected in the same way as a returning slot. 
+		*	so we call ExecProcessReturning() directly here.
+		*/
+		if(action_pstate->operation != CMD_DELETE)
+			actslot = ExecProcessReturning(action_pstate->ps.ps_ProjInfo, slot, planSlot);
+
+		switch (action_pstate->operation)
+		{
+			case CMD_INSERT:
+				res = ExecInsert(actslot, planSlot, estate);
+				break;
+			case CMD_UPDATE:
+				res = ExecUpdate(tupleid,
+							actslot,
+							planSlot,
+							&mt_pstate->mt_epqstate,
+							estate);
+				break;
+			case CMD_DELETE:
+				res = ExecDelete(tupleid, 
+							planSlot, 
+							&mt_pstate->mt_epqstate,
+							estate);
+				break;
+			default:
+				elog(ERROR, "unknown merge action type");
+				break;
+		}
+
+
+		/*
+		* The current action is executed, no need to do the remain actions
+		*/	
+		return res;
+	}
+
+	/*
+	* Here, no action is taken. Let's pass this slot
+	*/	
+	return NULL;
+	
+}
+
 /*
  * Process BEFORE EACH STATEMENT triggers
  */
@@ -603,6 +713,9 @@ fireBSTriggers(ModifyTableState *node)
 			ExecBSDeleteTriggers(node->ps.state,
 								 node->ps.state->es_result_relations);
 			break;
+		case CMD_MERGE:
+			printf("not sure about the BS triggers of merge\n");
+			break;
 		default:
 			elog(ERROR, "unknown operation");
 			break;
@@ -629,6 +742,9 @@ fireASTriggers(ModifyTableState *node)
 			ExecASDeleteTriggers(node->ps.state,
 								 node->ps.state->es_result_relations);
 			break;
+		case CMD_MERGE:
+			printf("not sure about the AS triggers of merge\n");
+			break;	
 		default:
 			elog(ERROR, "unknown operation");
 			break;
@@ -708,20 +824,34 @@ ExecModifyTable(ModifyTableState *node)
 			/*
 			 * extract the 'ctid' junk attribute.
 			 */
-			if (operation == CMD_UPDATE || operation == CMD_DELETE)
+			if (operation == CMD_UPDATE || operation == CMD_DELETE || operation == CMD_MERGE)
 			{
 				Datum		datum;
 				bool		isNull;
 
 				datum = ExecGetJunkAttribute(slot, junkfilter->jf_junkAttNo,
 											 &isNull);
-				/* shouldn't ever get a null result... */
+				
 				if (isNull)
-					elog(ERROR, "ctid is NULL");
-
-				tupleid = (ItemPointer) DatumGetPointer(datum);
-				tuple_ctid = *tupleid;	/* be sure we don't free the ctid!! */
-				tupleid = &tuple_ctid;
+				{
+					/*
+					*	shouldn't ever get a null result for update and delete. 
+					*	Merge command will get a null ctid in "NOT MATCHED" case
+					*/
+					if(operation != CMD_MERGE)
+						elog(ERROR, "ctid is NULL");
+					else
+						tupleid = NULL;
+				}	
+				else
+				{
+				
+					tupleid = (ItemPointer) DatumGetPointer(datum);
+					
+					tuple_ctid = *tupleid;	/* be sure we don't free the ctid!! */
+					tupleid = &tuple_ctid;
+					
+				}
 			}
 
 			/*
@@ -744,6 +874,11 @@ ExecModifyTable(ModifyTableState *node)
 				slot = ExecDelete(tupleid, planSlot,
 								  &node->mt_epqstate, estate);
 				break;
+			case CMD_MERGE:
+				slot = ExecMerge(tupleid, slot, planSlot,
+								  node, estate);
+				break;	
+				
 			default:
 				elog(ERROR, "unknown operation");
 				break;
@@ -771,6 +906,86 @@ ExecModifyTable(ModifyTableState *node)
 	return NULL;
 }
 
+
+/*
+*	When init a merge plan, we also need init its action plans. 
+*	These action plans are "MergeAction" plans (new plan node for the merge actions).
+*	
+*	In this function, we only want to handle the tlist and qual in the plan.
+*	The returning result is a  "MergeActionState".  
+*/
+MergeActionState *
+ExecInitMergeAction(MergeAction *node, EState *estate, int eflags)
+{
+	MergeActionState *result;
+	
+	/*
+	 * do nothing when we get to the end of a leaf on tree.
+	 */
+	if (node == NULL)
+		return NULL;
+
+		
+	/*
+	 * create state structure
+	 */
+	result = makeNode(MergeActionState);
+	result->operation = node->operation;
+	result->ps.plan = (Plan *)node;
+	result->ps.state = estate;
+
+	/*
+	 * tuple table initialization
+	 */
+	ExecInitResultTupleSlot(estate, &result->ps);
+
+
+	
+	/*
+	 * initialize tuple type 
+	 */
+	ExecAssignResultTypeFromTL(&result->ps);
+
+		
+	/*
+	 * create expression context for node
+	 */
+	 
+	ExecAssignExprContext(estate, &result->ps);
+
+
+	/*
+	 * initialize child expressions
+	 */
+	result->ps.targetlist = (List *)
+		ExecInitExpr((Expr *) node->plan.targetlist,  &result->ps);
+
+	
+	result->ps.qual = (List *)
+		ExecInitExpr((Expr *) node->plan.qual, &result->ps);
+
+	
+	/*
+	* init the projection information
+	*/
+	ExecAssignProjectionInfo(&result->ps, NULL);
+
+	/*
+	do we need a check for the plan output here ?
+	
+	if(estate->es_result_relation_info == NULL)
+		printf("re infro is null\n");
+
+	if(estate->es_result_relation_info->ri_RelationDesc == NULL)
+		printf("r relation desc is nUll\n");
+		ExecCheckPlanOutput(estate->es_result_relation_info->ri_RelationDesc,
+								node->targetlist);
+	printf("finish check plan output for merge actio \n");	
+	*/
+	return result;
+}
+
+
 /* ----------------------------------------------------------------
  *		ExecInitModifyTable
  * ----------------------------------------------------------------
@@ -786,6 +1001,7 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	Plan	   *subplan;
 	ListCell   *l;
 	int			i;
+	bool 		isMergeAction = false;
 
 	/* check for unsupported flags */
 	Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
@@ -826,6 +1042,16 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	foreach(l, node->plans)
 	{
 		subplan = (Plan *) lfirst(l);
+
+		/*
+		* 	test if this subplan node is a MergeAction. 
+		* 	We need this information for setting the junckfilter. 
+		*	juckfiler is necessary for an ordinary UPDATE/DELETE plan, 
+		*	but not for an UPDATE/DELETE merge action  
+		*/		
+		if(IsA(subplan, MergeAction))
+			isMergeAction = true;
+		
 		mtstate->mt_plans[i] = ExecInitNode(subplan, estate, eflags);
 		estate->es_result_relation_info++;
 		i++;
@@ -955,7 +1181,9 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 				break;
 			case CMD_UPDATE:
 			case CMD_DELETE:
-				junk_filter_needed = true;
+			case CMD_MERGE:	
+				if(!isMergeAction)
+					junk_filter_needed = true;
 				break;
 			default:
 				elog(ERROR, "unknown operation");
@@ -978,9 +1206,9 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 							resultRelInfo->ri_RelationDesc->rd_att->tdhasoid,
 									   ExecInitExtraTupleSlot(estate));
 
-				if (operation == CMD_UPDATE || operation == CMD_DELETE)
+				if (operation == CMD_UPDATE || operation == CMD_DELETE || operation == CMD_MERGE)
 				{
-					/* For UPDATE/DELETE, find the ctid junk attr now */
+					/* For UPDATE/DELETE/MERGE, find the ctid junk attr now */
 					j->jf_junkAttNo = ExecFindJunkAttribute(j, "ctid");
 					if (!AttributeNumberIsValid(j->jf_junkAttNo))
 						elog(ERROR, "could not find junk ctid column");
@@ -1006,6 +1234,21 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	if (estate->es_trig_tuple_slot == NULL)
 		estate->es_trig_tuple_slot = ExecInitExtraTupleSlot(estate);
 
+	
+	/*
+	* for the merge actions, we need to similar things as above
+	*/
+
+	foreach(l, node->mergeActPlan)
+	{
+		PlanState *actpstate = ExecInitNode((Plan *)lfirst(l),  estate, 0);
+		/*
+		* put the pstates of each action into ModifyTableState
+		*/
+		mtstate->mergeActPstates = lappend(mtstate->mergeActPstates, actpstate);
+		
+	}
+	
 	return mtstate;
 }
 
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 93dcef5..13f2153 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -176,6 +176,7 @@ _copyModifyTable(ModifyTable *from)
 	COPY_NODE_FIELD(returningLists);
 	COPY_NODE_FIELD(rowMarks);
 	COPY_SCALAR_FIELD(epqParam);
+	COPY_NODE_FIELD(mergeActPlan);
 
 	return newnode;
 }
@@ -2273,6 +2274,10 @@ _copyQuery(Query *from)
 	COPY_NODE_FIELD(rowMarks);
 	COPY_NODE_FIELD(setOperations);
 
+	COPY_SCALAR_FIELD(isMergeAction);
+	/*merge action list*/
+	COPY_NODE_FIELD(mergeActQry); 
+
 	return newnode;
 }
 
@@ -2343,6 +2348,64 @@ _copySelectStmt(SelectStmt *from)
 	return newnode;
 }
 
+
+static MergeStmt *
+_copyMergeStmt(MergeStmt *from)
+{
+	MergeStmt *newnode = makeNode(MergeStmt);
+
+	COPY_NODE_FIELD(relation);
+	COPY_NODE_FIELD(source);
+	COPY_NODE_FIELD(matchCondition);
+	COPY_NODE_FIELD(actions);
+	
+	return newnode;
+	
+}
+
+
+static MergeConditionAction *
+_copyMergeConditionAction(MergeConditionAction *from)
+{
+	MergeConditionAction *newnode = makeNode(MergeConditionAction);
+
+	COPY_SCALAR_FIELD(match);
+	COPY_NODE_FIELD(condition);
+	COPY_NODE_FIELD(action);
+
+	return newnode;
+}
+
+static MergeUpdate *
+_copyMergeUpdate(MergeUpdate *from)
+{
+	MergeUpdate *newNode = (MergeUpdate *)_copyUpdateStmt((UpdateStmt *) from);
+	newNode->type = T_MergeUpdate;
+
+	return newNode;
+}
+
+static MergeInsert *
+_copyMergeInsert(MergeInsert *from)
+{
+	MergeInsert *newNode = (MergeInsert *)_copyInsertStmt((InsertStmt *) from);
+	newNode->type = T_MergeInsert;
+
+	return newNode;
+}
+
+
+static MergeDelete *
+_copyMergeDelete(MergeDelete *from)
+{
+	MergeDelete *newNode = (MergeDelete *)_copyDeleteStmt((DeleteStmt *) from);
+	newNode->type = T_MergeDelete;
+
+	return newNode;
+}
+
+
+
 static SetOperationStmt *
 _copySetOperationStmt(SetOperationStmt *from)
 {
@@ -3903,6 +3966,21 @@ copyObject(void *from)
 		case T_SelectStmt:
 			retval = _copySelectStmt(from);
 			break;
+		case T_MergeStmt:
+			retval = _copyMergeStmt(from);
+			break;
+		case T_MergeConditionAction:
+			retval = _copyMergeConditionAction(from);
+			break;
+		case T_MergeUpdate:
+			retval = _copyMergeUpdate(from);
+			break;
+		case T_MergeInsert:
+			retval = _copyMergeInsert(from);
+			break;
+		case T_MergeDelete:
+			retval = _copyMergeDelete(from);
+			break;
 		case T_SetOperationStmt:
 			retval = _copySetOperationStmt(from);
 			break;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 5d83727..572f6df 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -878,6 +878,7 @@ _equalQuery(Query *a, Query *b)
 	COMPARE_NODE_FIELD(rowMarks);
 	COMPARE_NODE_FIELD(setOperations);
 
+	COMPARE_SCALAR_FIELD(isMergeAction);
 	return true;
 }
 
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 79baf4f..339b79f 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -331,6 +331,7 @@ _outModifyTable(StringInfo str, ModifyTable *node)
 	WRITE_NODE_FIELD(returningLists);
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_INT_FIELD(epqParam);
+	WRITE_NODE_FIELD(mergeActPlan);
 }
 
 static void
@@ -2019,8 +2020,60 @@ _outQuery(StringInfo str, Query *node)
 	WRITE_NODE_FIELD(limitCount);
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_NODE_FIELD(setOperations);
+	WRITE_BOOL_FIELD(isMergeAction);
+	WRITE_NODE_FIELD(mergeActQry);
 }
 
+
+static void
+_outMergeConditionAction(StringInfo str, MergeConditionAction *node)
+{
+	WRITE_NODE_TYPE("MERGECONDITIONACTION");
+
+	WRITE_BOOL_FIELD(match);
+	
+	WRITE_NODE_FIELD(condition);
+	WRITE_NODE_FIELD(action);
+
+
+}
+
+static void
+_outMergeStmt(StringInfo str, MergeStmt *node)
+{
+	WRITE_NODE_TYPE("MERGESTMT");
+
+	WRITE_NODE_FIELD(relation);
+	WRITE_NODE_FIELD(source);
+	WRITE_NODE_FIELD(matchCondition);
+	WRITE_NODE_FIELD(actions);
+
+}
+
+static void
+_outMergeAction(StringInfo str, MergeAction*node)
+{
+	_outPlanInfo(str, (Plan *)node);
+
+	WRITE_ENUM_FIELD(operation, CmdType);
+
+}
+
+static void 
+_outDeleteStmt(StringInfo str, DeleteStmt *node)
+{
+	WRITE_NODE_TYPE("DELETESTMT");
+
+	WRITE_NODE_FIELD(relation);
+	WRITE_NODE_FIELD(usingClause);
+	WRITE_NODE_FIELD(whereClause);
+	WRITE_NODE_FIELD(returningList);
+
+
+}
+
+
+
 static void
 _outSortGroupClause(StringInfo str, SortGroupClause *node)
 {
@@ -2904,6 +2957,19 @@ _outNode(StringInfo str, void *obj)
 			case T_XmlSerialize:
 				_outXmlSerialize(str, obj);
 				break;
+			case T_MergeAction:
+				_outMergeAction(str, obj);
+				break;
+			case T_MergeStmt:
+				_outMergeStmt(str, obj);
+				break;
+			case T_MergeConditionAction:
+				_outMergeConditionAction(str,obj);
+				break;
+			case T_DeleteStmt:
+				_outDeleteStmt(str,obj);
+				break;
+					
 
 			default:
 
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index bc6e2a6..b792132 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -218,7 +218,9 @@ _readQuery(void)
 	READ_NODE_FIELD(limitCount);
 	READ_NODE_FIELD(rowMarks);
 	READ_NODE_FIELD(setOperations);
-
+	READ_BOOL_FIELD(isMergeAction);
+	READ_NODE_FIELD(mergeActQry);
+	
 	READ_DONE();
 }
 
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 3950ab4..0057547 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -565,6 +565,26 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 											 returningLists,
 											 rowMarks,
 											 SS_assign_special_param(root));
+
+			/*do a simple plan for each actions in the merge command.
+			*put them in mergeActPlan list;
+			*/
+			if(parse->commandType == CMD_MERGE)
+			{
+				ListCell *l;
+				ModifyTable *top_plan = (ModifyTable *)plan;
+				foreach(l, parse->mergeActQry)
+				{
+					
+					Plan *actplan = (Plan *)merge_action_planner(glob, 
+																		(Query *)lfirst(l),
+																		(Plan *)linitial(top_plan->plans)
+																	);
+
+					top_plan->mergeActPlan = lappend(top_plan->mergeActPlan, actplan);
+				}
+
+			}
 		}
 	}
 
@@ -584,6 +604,109 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	return plan;
 }
 
+
+
+ModifyTable *
+merge_action_planner(PlannerGlobal *glob, Query *parse,
+				 Plan *top_plan)
+{
+	PlannerInfo *root;
+	MergeAction	*actplan;
+	ModifyTable *result;
+	
+	List	   	*returningLists;
+	List 		*rowMarks;
+
+	/*
+	 * no having clause in a merge action
+	 */
+	Assert(parse->havingQual == NULL);
+
+
+	/* Create a PlannerInfo data structure for this subquery */
+	root = makeNode(PlannerInfo);
+	root->parse = parse;
+	root->glob = glob;
+	root->query_level = 1;
+	root->parent_root = NULL;
+	root->planner_cxt = CurrentMemoryContext;
+	root->init_plans = NIL;
+	root->cte_plan_ids = NIL;
+	root->eq_classes = NIL;
+	root->append_rel_list = NIL;
+	root->hasPseudoConstantQuals = false;
+	root->hasRecursion = false;
+	root->wt_param_id = -1;
+	root->non_recursive_plan = NULL;
+
+
+	/*
+	*	Create the action plan node
+	*/
+	actplan = makeNode(MergeAction);
+	actplan->operation = parse->commandType;
+	
+	/*
+	 * Do expression preprocessing on targetlist and quals.
+	 */
+	parse->targetList = (List *)
+		preprocess_expression(root, (Node *) parse->targetList,
+							  EXPRKIND_TARGET);
+
+	preprocess_qual_conditions(root, (Node *) parse->jointree);
+	
+
+	/*
+	*	we need a flat qual for explaining
+	*/	
+	actplan->flattenedqual = flatten_join_alias_vars(root, parse->jointree->quals);
+	
+	/*copy the cost from the top_plan*/
+	actplan->plan.startup_cost = top_plan->startup_cost;
+	actplan->plan.total_cost = top_plan->total_cost;
+	actplan->plan.plan_rows = top_plan->plan_rows;
+	actplan->plan.plan_width = top_plan->plan_width;
+	
+	/*
+	*	prepare the result 
+	*/
+	actplan->plan.targetlist = preprocess_targetlist(root,parse->targetList);
+
+	actplan->plan.qual = (List *)parse->jointree->quals;
+	push_up_merge_action_vars(actplan, parse);
+
+	if (parse->returningList)
+	{
+		List	   *rlist;
+
+		Assert(parse->resultRelation);
+		rlist = set_returning_clause_references(root->glob,
+												parse->returningList,
+												&actplan->plan,
+											  parse->resultRelation);
+		returningLists = list_make1(rlist);
+	}
+	else
+		returningLists = NIL;
+
+
+	if (parse->rowMarks)
+		rowMarks = NIL;
+	else
+		rowMarks = root->rowMarks;
+	
+	result = make_modifytable(parse->commandType,
+										   copyObject(root->resultRelations),
+											 list_make1(actplan),
+											 returningLists,
+											 rowMarks,
+											 SS_assign_special_param(root));
+
+	
+	return result;
+}
+
+
 /*
  * preprocess_expression
  *		Do subquery_planner's preprocessing work for an expression,
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
index 59d3518..5685d52 100644
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -78,13 +78,20 @@ preprocess_targetlist(PlannerInfo *root, List *tlist)
 								  result_relation, range_table);
 
 	/*
-	 * for "update" and "delete" queries, add ctid of the result relation into
+	 * for "update" , "delete"  and "merge" queries, add ctid of the result relation into
 	 * the target list so that the ctid will propagate through execution and
 	 * ExecutePlan() will be able to identify the right tuple to replace or
 	 * delete.	This extra field is marked "junk" so that it is not stored
 	 * back into the tuple.
+	 *  
+	 * BUT, if the query node is a merge action, we don't need to expend the ctid attribute in tlist.
+	 * The tlist of the merge top level plan already contains a "ctid" junk attr of the target relation.
 	 */
-	if (command_type == CMD_UPDATE || command_type == CMD_DELETE)
+	 
+	if(!parse->isMergeAction  &&  
+			(command_type == CMD_UPDATE || 
+			command_type == CMD_DELETE || 
+			command_type == CMD_MERGE))
 	{
 		TargetEntry *tle;
 		Var		   *var;
diff --git a/src/backend/optimizer/util/var.c b/src/backend/optimizer/util/var.c
index 92c2208..f1fcbaa 100644
--- a/src/backend/optimizer/util/var.c
+++ b/src/backend/optimizer/util/var.c
@@ -67,6 +67,16 @@ typedef struct
 	bool		inserted_sublink;		/* have we inserted a SubLink? */
 } flatten_join_alias_vars_context;
 
+typedef struct
+{
+	int varno_source;
+	int varno_target;
+	int varno_join;
+
+	int offset_source;
+	int offset_target;
+} push_up_merge_action_vars_context;
+
 static bool pull_varnos_walker(Node *node,
 				   pull_varnos_context *context);
 static bool pull_varattnos_walker(Node *node, Bitmapset **varattnos);
@@ -83,6 +93,8 @@ static bool pull_var_clause_walker(Node *node,
 static Node *flatten_join_alias_vars_mutator(Node *node,
 								flatten_join_alias_vars_context *context);
 static Relids alias_relid_set(PlannerInfo *root, Relids relids);
+static bool push_up_merge_action_vars_walker(Node *node, 
+								push_up_merge_action_vars_context *context);
 
 
 /*
@@ -677,6 +689,88 @@ pull_var_clause_walker(Node *node, pull_var_clause_context *context)
 								  (void *) context);
 }
 
+/*
+*	When prepare for the MERGE command, we have made a left join between the 
+*	source table and target table as the main plan. In this case, the range table contains 
+*	ONLY THREE range table entries: 
+*	The first one is that of the source table, which may be a subquery or a plain table
+*	The second one is the entry of the targe table, which is a plain table
+*	The third one is a join expression with the sourse table and target table as its parameters.
+*
+*	Each merge action of the command has its own query and plan nodes as well. And, the vars 
+*	in its target list and qual expressions may refers to the attribute in any one of the above 3 
+* 	range table entries.
+*	
+*	However, since the result tuple slots of merge actions are projected from the returned tuple of
+*	the join, we need to mapping the vars of source table and target table to their corresponding 
+*	attributes in the third range table entry. 
+*
+*	This function does the opposit of the flatten_join_alias_vars() function. It walks through the 
+*	target list and qual of a MergeAction plan, changes the vars' varno and varattno to the 
+*	corresponding position in the upper level join RTE.
+*	
+*/
+void 
+push_up_merge_action_vars(MergeAction *actplan, Query *actqry)
+{
+	push_up_merge_action_vars_context context;
+	RangeTblEntry *source_rte = rt_fetch(1,actqry->rtable);
+
+
+	/*
+	* 	We are supposed to do a  more careful assingment of the values in context
+	*	But lets take a shortcut for simple.
+	*/
+	context.varno_source = 1;
+	context.varno_target = 2;
+	context.varno_join = 3;
+
+	context.offset_source = 0;
+
+	
+	context.offset_target = list_length(source_rte->eref->colnames);
+
+	push_up_merge_action_vars_walker(actplan->plan.targetlist, &context);
+	
+	push_up_merge_action_vars_walker(actplan->plan.qual, &context);
+	
+}
+
+
+static bool
+push_up_merge_action_vars_walker(Node *node, 
+									push_up_merge_action_vars_context *context)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, Var))
+	{
+		Var *var = (Var *)node;
+
+		if(var->varno == context->varno_source)
+		{
+			var->varno = context->varno_join;
+			var->varattno += context->offset_source;
+			return false;
+		}
+		else if(var->varno == context->varno_target)
+		{
+			var->varno = context->varno_join;
+			var->varattno += context->offset_target;
+			return false;
+		}
+		else if(var->varno == context->varno_join)
+			return false;
+		else
+			elog(ERROR, "the vars in merge action tlist of qual should only belongs to the source table or targe table");
+		
+		
+	}
+	
+	return expression_tree_walker(node, push_up_merge_action_vars_walker,
+								  (void *) context);
+}
+
 
 /*
  * flatten_join_alias_vars
diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 6b99a10..58d7a49 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -47,6 +47,7 @@ static Query *transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt);
 static Query *transformInsertStmt(ParseState *pstate, InsertStmt *stmt);
 static List *transformInsertRow(ParseState *pstate, List *exprlist,
 				   List *stmtcols, List *icolumns, List *attrnos);
+static Query *transformMergeStmt(ParseState *pstate, MergeStmt *stmt);
 static Query *transformSelectStmt(ParseState *pstate, SelectStmt *stmt);
 static Query *transformValuesClause(ParseState *pstate, SelectStmt *stmt);
 static Query *transformSetOperationStmt(ParseState *pstate, SelectStmt *stmt);
@@ -164,17 +165,24 @@ transformStmt(ParseState *pstate, Node *parseTree)
 			 * Optimizable statements
 			 */
 		case T_InsertStmt:
+		case T_MergeInsert:
 			result = transformInsertStmt(pstate, (InsertStmt *) parseTree);
 			break;
 
 		case T_DeleteStmt:
+		case T_MergeDelete:
 			result = transformDeleteStmt(pstate, (DeleteStmt *) parseTree);
 			break;
 
 		case T_UpdateStmt:
+		case T_MergeUpdate:
 			result = transformUpdateStmt(pstate, (UpdateStmt *) parseTree);
 			break;
 
+		case T_MergeStmt:
+			result = transformMergeStmt(pstate, (MergeStmt *)parseTree);
+			break; 
+
 		case T_SelectStmt:
 			{
 				SelectStmt *n = (SelectStmt *) parseTree;
@@ -282,22 +290,33 @@ transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt)
 
 	qry->commandType = CMD_DELETE;
 
-	/* set up range table with just the result rel */
-	qry->resultRelation = setTargetTable(pstate, stmt->relation,
-								  interpretInhOption(stmt->relation->inhOpt),
-										 true,
-										 ACL_DELETE);
-
 	qry->distinctClause = NIL;
 
+	if(IsA(stmt,MergeDelete))
+		qry->isMergeAction = true;
 	/*
-	 * The USING clause is non-standard SQL syntax, and is equivalent in
-	 * functionality to the FROM list that can be specified for UPDATE. The
-	 * USING keyword is used rather than FROM because FROM is already a
-	 * keyword in the DELETE syntax.
-	 */
-	transformFromClause(pstate, stmt->usingClause);
+	* The input stmt could be a MergeDelete node. 
+	* In this case, we don't need the process on range table.
+	*/
+	if(IsA(stmt, DeleteStmt))
+	{
+		/* set up range table with just the result rel */
+		qry->resultRelation = setTargetTable(pstate, stmt->relation,
+									  interpretInhOption(stmt->relation->inhOpt),
+											 true,
+											 ACL_DELETE);
 
+		
+
+		/*
+		 * The USING clause is non-standard SQL syntax, and is equivalent in
+		 * functionality to the FROM list that can be specified for UPDATE. The
+		 * USING keyword is used rather than FROM because FROM is already a
+		 * keyword in the DELETE syntax.
+		 */
+		transformFromClause(pstate, stmt->usingClause);
+	}
+	
 	qual = transformWhereClause(pstate, stmt->whereClause, "WHERE");
 
 	qry->returningList = transformReturningList(pstate, stmt->returningList);
@@ -342,11 +361,16 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 	qry->commandType = CMD_INSERT;
 	pstate->p_is_insert = true;
 
+	if(IsA(stmt,MergeInsert))
+		qry->isMergeAction = true;
+	
 	/*
 	 * We have three cases to deal with: DEFAULT VALUES (selectStmt == NULL),
 	 * VALUES list, or general SELECT input.  We special-case VALUES, both for
 	 * efficiency and so we can handle DEFAULT specifications.
 	 */
+
+	/*a MergeInsert statment is always a VALUE clause*/
 	isGeneralSelect = (selectStmt && selectStmt->valuesLists == NIL);
 
 	/*
@@ -382,7 +406,8 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 	 * mentioned in the SELECT part.  Note that the target table is not added
 	 * to the joinlist or namespace.
 	 */
-	qry->resultRelation = setTargetTable(pstate, stmt->relation,
+	if(IsA(stmt,InsertStmt))/*for MergeInsert, no need to do this*/ 
+		qry->resultRelation = setTargetTable(pstate, stmt->relation,
 										 false, false, ACL_INSERT);
 
 	/* Validate stmt->cols list, or build default list if no list given */
@@ -1730,16 +1755,23 @@ transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt)
 	qry->commandType = CMD_UPDATE;
 	pstate->p_is_update = true;
 
-	qry->resultRelation = setTargetTable(pstate, stmt->relation,
-								  interpretInhOption(stmt->relation->inhOpt),
-										 true,
-										 ACL_UPDATE);
+	if(IsA(stmt,MergeUpdate))
+		qry->isMergeAction = true;
 
-	/*
-	 * the FROM clause is non-standard SQL syntax. We used to be able to do
-	 * this with REPLACE in POSTQUEL so we keep the feature.
-	 */
-	transformFromClause(pstate, stmt->fromClause);
+	
+	if(IsA(stmt, UpdateStmt))/*for MergeUpdate, no need to do this*/
+	{
+		qry->resultRelation = setTargetTable(pstate, stmt->relation,
+									  interpretInhOption(stmt->relation->inhOpt),
+											 true,
+											 ACL_UPDATE);
+
+		/*
+		 * the FROM clause is non-standard SQL syntax. We used to be able to do
+		 * this with REPLACE in POSTQUEL so we keep the feature.
+		 */
+		transformFromClause(pstate, stmt->fromClause);
+	}
 
 	qry->targetList = transformTargetList(pstate, stmt->targetList);
 
@@ -2241,3 +2273,304 @@ applyLockingClause(Query *qry, Index rtindex,
 	rc->pushedDown = pushedDown;
 	qry->rowMarks = lappend(qry->rowMarks, rc);
 }
+
+
+
+/*transform a action of merge command into a query. 
+No change of the pstate range table is allowed in this function. 
+*/
+static Query *
+transformMergeActions(ParseState *pstate, MergeStmt *stmt, MergeConditionAction *condact)
+{
+	Query *actqry = makeNode(Query);
+	A_Expr *match_expr; 
+	A_Expr *act_qual_expr;
+
+	/*
+	*	firstly, we need to make sure that DELETE and UPDATE 
+	*	actions are only taken in MATCHED condition, 
+	*	and INSERTs are only takend when not MATCHED
+	*/
+	if(IsA(condact->action, MergeDelete)) 
+	{	
+		if(!condact->match) 
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+		 		errmsg("The DELETE action in MERGE command is not allowed when NOT MATCHED")));
+	}
+	else if(IsA(condact->action, MergeUpdate))
+	{	
+		if(!condact->match) 
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+		 		errmsg("The UPDATE action in MERGE command is not allowed when NOT MATCHED")));
+	}
+	else if(IsA(condact->action, MergeInsert))
+	{	
+		if(condact->match) 
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+		 		errmsg("The INSERT action in MERGE command is not allowed when MATCHED")));
+	}
+	else
+		ereport(ERROR,
+			(errcode(ERRCODE_SYNTAX_ERROR),
+			 errmsg("UNKONWN action type in MERGE")));
+
+
+		
+	act_qual_expr = condact->condition;
+	
+	/*use the transfomStmt() to parse all types of actions*/
+	if(IsA(condact->action, MergeDelete))
+	{
+		/*a delete action*/
+		MergeDelete *deleteact = (MergeDelete *)(condact->action);
+		Assert(IsA(deleteact,DeleteStmt));
+		
+		deleteact->relation = stmt->relation;
+		deleteact->usingClause = stmt->source;
+		deleteact->whereClause = (Node *)act_qual_expr;
+
+		/*parse the action query*/
+		actqry = transformStmt(pstate, (Node *)deleteact);
+
+		if(!IsA(actqry, Query) || actqry->commandType != CMD_DELETE || actqry->utilityStmt != NULL)
+			elog(ERROR, "improper DELETE action in merge stmt");
+
+		return actqry;
+	}
+	else if(IsA(condact->action, MergeUpdate))
+	{
+		/*an update action*/
+		MergeUpdate *updateact = (MergeUpdate *)(condact->action);
+
+		/*the "targetlist" of the updateact is filled in the parser */
+		updateact->relation = stmt->relation;
+		updateact->fromClause = stmt->source;
+		updateact->whereClause = (Node *)act_qual_expr;
+
+		/*parse the action query*/
+		actqry = transformStmt(pstate, (Node *)updateact);
+
+		if(!IsA(actqry, Query) || actqry->commandType != CMD_UPDATE|| actqry->utilityStmt != NULL)
+			elog(ERROR, "improper UPDATE action in merge stmt");
+
+		return actqry;
+	}
+	else if(IsA(condact->action, MergeInsert))
+	{
+		/*an insert action*/
+		Node *qual;
+		MergeInsert *insertact;
+
+		insertact = (MergeInsert *)(condact->action);
+		
+		
+		/*the "cols" and "selectStmt" of the insertact is filled in the parser */
+		insertact->relation = stmt->relation;
+
+		/*
+		the merge insert action has a strange feature. 
+		In an ordinary INSERT, the VALUES list can only contains constants and DEFAULT. (am I right??)
+		But in the INSERT action of MERGE command, the VALUES list can have expressions with variables(attributes of the targe and source tables).
+		Besides, in the ordinary INSERT, a VALUES list can never be followed by a WHERE clause. But in MERGE INSERT action, there are matching conditions. 
+
+		Thus, the output qry of this function is an INSERT query in the style of "INSERT...VALUES...", except that we have other range tables and a WHERE clause.
+		Note that it is also different from the "INSERT ... SELECT..." query, in which the whole SELECT is a subquery. (We don't have subquery here).
+		We construct this novel query structure in order to keep consitency with other merge action types (DELETE, UPDATE). 
+		In this way, all the merge action queries are in fact share the very same Range Table, They only differs in their target lists and join trees
+		
+		*/
+		
+				
+		/*parse the action query, this will call transformInsertStmt() which analyzes the VALUES list.*/
+		actqry = transformStmt(pstate, (Node *)insertact);
+
+		/*do the WHERE clause here, Since the transformInsertStmt() function 
+		only analyzes the VALUES list but not the WHERE clause*/
+		qual = transformWhereClause(pstate,(Node *)act_qual_expr, "WHERE");
+		
+		actqry->jointree = makeFromExpr(pstate->p_joinlist, qual);
+
+		if(!IsA(actqry, Query) || actqry->commandType != CMD_INSERT|| actqry->utilityStmt != NULL)
+			elog(ERROR, "improper INSERT action in merge stmt");
+
+
+		return actqry;
+	}
+	else
+		elog(ERROR, "unknown action type in MERGE");
+
+	/*never comes here*/
+	return NULL;
+}
+
+
+
+static Query *
+transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
+{
+	Query	   *qry; 
+
+	ColumnRef *starRef;
+	ResTarget *starResTarget;
+	ListCell *act;
+	ListCell *l;
+	JoinExpr *joinexp;
+	int 	rtindex;
+
+	/*this will never happen, since the garm.y is restricted that only one rel name is allowed to appear in the source table position. 
+	However, if we extent the command in future, we may need to note this check here. 
+	*/
+	if(list_length(stmt->source) != 1) 
+		ereport(ERROR,
+			(errcode(ERRCODE_SYNTAX_ERROR),
+			 errmsg("now we only accept merge command with only ONE source table")));
+		
+	/*now, do the real tranformation of the merge command. */
+	qry = makeNode(Query);
+	qry->commandType = CMD_MERGE;
+
+	/*
+	What we are doing here is to create a query like 
+		"SELECT * FROM <source_rel> LEFT JOIN <target_rel> ON <match_condition>;"
+	Note:	
+	1. we set the "match condition" as the join qualification. 
+	The left join will scan both the matched and non-matched tuples.
+
+	2. a normal SELECT query has no "target relation". 
+	But here we need to set the targe relation in query, like the UPDATE/DELETE/INSERT queries. 
+	So this is a left join SELECT with a "target table" in its range table. 
+
+	3. We don't have a specific ACL level for Merge, here we just use ACL_SELECT. 
+	But we will add other ACL levels when handle each merge actions.  
+	*/
+
+
+	/*before analyze the FROM clause, we need to set the target table. 
+	We cannot call setTargetTable() function directly. 
+	We only need the lock target relation, without adding it to Range table. 
+	*/
+	
+	
+	setTargetTableLock(pstate, stmt->relation);
+	
+	
+	
+	/*create the FROM clause. Make the join expression first*/
+	joinexp = makeNode(JoinExpr);
+	joinexp->jointype = JOIN_LEFT;
+	joinexp->isNatural = FALSE;
+	joinexp->larg = linitial(stmt->source);/*source list has only one element*/
+	joinexp->rarg = (Node *)stmt->relation;
+	joinexp->quals = stmt->matchCondition; /*match condtion*/
+
+	/*transform the FROM clause. The target relation and source relation will be add to Rtable here.	*/
+	transformFromClause(pstate, list_make1(joinexp));
+
+	/*the targetList of the main query is "*"	  
+	*/
+	starRef = makeNode(ColumnRef);	
+	starRef->fields = list_make1(makeNode(A_Star));					
+	starRef->location = 1;					
+
+	starResTarget = makeNode(ResTarget);					
+	starResTarget->name = NULL;					
+	starResTarget->indirection = NIL;					
+	starResTarget->val = (Node *)starRef;					
+	starResTarget->location = 1;
+	
+	qry->targetList = transformTargetList(pstate, list_make1(starResTarget));
+
+	/*we don't need the WHERE clause here. Set it null. */
+	qry->jointree = makeFromExpr(pstate->p_joinlist, NULL);
+
+	/*now , we find out the RTE for the target relation, and do some unfinished jobs*/
+	rtindex = 1;
+	foreach(l, pstate->p_rtable)
+	{
+		RangeTblEntry *rte = (RangeTblEntry *)lfirst(l);
+		if(rte->relid == pstate->p_target_relation->rd_id) /*find the RTE*/
+		{
+			pstate->p_target_rangetblentry = rte;
+			rte->requiredPerms = ACL_SELECT;	
+			qry->resultRelation = rtindex;
+			break;
+		}
+		rtindex++;
+	}
+
+	if(pstate->p_target_rangetblentry == NULL)
+		elog(ERROR, "cannot find the RTE for target table");
+	
+
+	qry->rtable = pstate->p_rtable;
+
+	qry->hasSubLinks = pstate->p_hasSubLinks;
+
+	/*
+	 * Top-level aggregates are simply disallowed in MERGE
+	 */
+	if (pstate->p_hasAggs)
+		ereport(ERROR,
+				(errcode(ERRCODE_GROUPING_ERROR),
+				 errmsg("cannot use aggregate function in top level of MERGE"),
+				 parser_errposition(pstate,
+									locate_agg_of_level((Node *) qry, 0))));
+	if (pstate->p_hasWindowFuncs)
+		ereport(ERROR,
+				(errcode(ERRCODE_WINDOWING_ERROR),
+				 errmsg("cannot use window function in MERGE"),
+				 parser_errposition(pstate,
+									locate_windowfunc((Node *) qry))));
+
+
+	/*
+		the main query is done.
+	then for each actions ,we transform it to a seperate query.
+	the action queries shares the exactly same range table with the main query. 
+	in other words, in the extra condtions of the sub actions, we don't allow involvement of new tables
+	*/
+	
+	qry->mergeActQry = NIL;
+
+	foreach(act,stmt->actions)
+	{
+		MergeConditionAction *mca = lfirst(act);
+		Query *actqry;
+
+		switch(mca->action->type)
+		{
+			case T_MergeDelete:
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_DELETE;
+				break;
+			case T_MergeUpdate:
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_UPDATE;
+				break;
+			case T_MergeInsert:
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_INSERT;				
+				break;
+			default:
+				elog(ERROR, "unknown MERGE action type %d", mca->type);
+				break;
+
+		}
+
+
+		/*transform the act (and its condition) as a single query. Link it to the top-level query*/
+		actqry = transformMergeActions(pstate, stmt, mca);
+
+		/*since we don't invoke setTargetTable() in transformMergeActions(), we need to set actqry->resultRelation here
+		*/
+		actqry->resultRelation = qry->resultRelation;
+
+		qry->mergeActQry = lappend(qry->mergeActQry, actqry);
+	}
+	
+	return qry;
+
+	
+}
+
+
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 3f6eeeb..abf772c 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -212,6 +212,10 @@ static TypeName *TableFuncTypeName(List *columns);
 		DropOwnedStmt ReassignOwnedStmt
 		AlterTSConfigurationStmt AlterTSDictionaryStmt
 
+%type <node>	MergeStmt  opt_and_condition  merge_condition_action   merge_action
+%type <boolean> opt_not	
+%type <list> 	merge_condition_action_list
+
 %type <node>	select_no_parens select_with_parens select_clause
 				simple_select values_clause
 
@@ -504,6 +508,8 @@ static TypeName *TableFuncTypeName(List *columns);
 
 	MAPPING MATCH MAXVALUE MINUTE_P MINVALUE MODE MONTH_P MOVE
 
+	MATCHED MERGE
+	
 	NAME_P NAMES NATIONAL NATURAL NCHAR NEXT NO NOCREATEDB
 	NOCREATEROLE NOCREATEUSER NOINHERIT NOLOGIN_P NONE NOSUPERUSER
 	NOT NOTHING NOTIFY NOTNULL NOWAIT NULL_P NULLIF NULLS_P NUMERIC
@@ -725,6 +731,7 @@ stmt :
 			| ListenStmt
 			| LoadStmt
 			| LockStmt
+			| MergeStmt 
 			| NotifyStmt
 			| PrepareStmt
 			| ReassignOwnedStmt
@@ -6952,6 +6959,7 @@ ExplainableStmt:
 			| InsertStmt
 			| UpdateStmt
 			| DeleteStmt
+			| MergeStmt
 			| DeclareCursorStmt
 			| CreateAsStmt
 			| ExecuteStmt					/* by default all are $$=$1 */
@@ -7297,6 +7305,101 @@ set_target_list:
 /*****************************************************************************
  *
  *		QUERY:
+ *				MERGE STATEMENT
+ *
+ *****************************************************************************/
+
+
+MergeStmt: 
+			MERGE INTO relation_expr_opt_alias
+			USING  table_ref
+			ON a_expr
+			merge_condition_action_list
+				{
+					MergeStmt *m = makeNode(MergeStmt);
+
+					m->relation = $3;
+					m->source = list_make1($5);  /*although we have only one USING table, but we still make it a list, maybe in future we will allow mutliple USING tables.*/
+					m->matchCondition = $7;
+					m->actions = $8;
+
+					$$ = (Node *)m;
+				}
+				;
+	
+merge_condition_action_list: 
+							merge_condition_action 		
+								{ $$ = list_make1($1); }
+							| merge_condition_action_list merge_condition_action   
+								{ $$ = lappend($1,$2); }
+							;	
+
+merge_condition_action: 	
+							WHEN opt_not MATCHED opt_and_condition THEN merge_action
+							{
+								MergeConditionAction *m = makeNode(MergeConditionAction);
+
+								m->match = $2;
+								m->condition = $4;
+								m->action = $6;
+
+								$$ = (Node *)m;
+							}
+							;
+
+
+opt_and_condition:	
+					AND a_expr 		{$$ = $2;}
+					| /*EMPTY*/ 		{$$ = NULL;}
+					;
+
+opt_not:	
+			NOT			{$$ = false;}
+			| /*EMPTY*/	{$$ = true;}
+			;
+
+merge_action: 	
+				DELETE_P	
+					{$$ = (Node *)makeNode(MergeDelete);}
+				| UPDATE SET set_clause_list 
+					{
+						UpdateStmt *n = makeNode(MergeUpdate);
+						n->targetList = $3;
+						$$ = (Node *)n;
+					}
+				| INSERT values_clause
+					{
+						InsertStmt *n = makeNode(MergeInsert);
+						n->cols = NIL;
+						n->selectStmt = $2;
+
+						$$ = (Node *)n;
+					}
+					
+				| INSERT '(' insert_column_list ')' values_clause
+					{
+						InsertStmt *n = makeNode(MergeInsert);
+						n->cols = $3;
+						n->selectStmt = $5;
+
+						$$ = (Node *)n;
+					}
+				| INSERT DEFAULT VALUES
+					{
+						InsertStmt *n = makeNode(MergeInsert);
+						n->cols = NIL;
+						n->selectStmt = NULL;
+
+						$$ = (Node *)n; 
+					}
+					
+				;	
+				
+
+
+/*****************************************************************************
+ *
+ *		QUERY:
  *				CURSOR STATEMENTS
  *
  *****************************************************************************/
@@ -10935,7 +11038,9 @@ unreserved_keyword:
 			| LOGIN_P
 			| MAPPING
 			| MATCH
+			| MATCHED
 			| MAXVALUE
+			| MERGE
 			| MINUTE_P
 			| MINVALUE
 			| MODE
diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index f30132a..657dd9c 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -213,6 +213,29 @@ setTargetTable(ParseState *pstate, RangeVar *relation,
 	return rtindex;
 }
 
+
+void
+setTargetTableLock(ParseState *pstate, RangeVar *relation)
+{
+	
+	/* Close old target; this could only happen for multi-action rules */
+	if (pstate->p_target_relation != NULL)
+		heap_close(pstate->p_target_relation, NoLock);
+
+	/*
+	 * Open target rel and grab suitable lock (which we will hold till end of
+	 * transaction).
+	 *
+	 * free_parsestate() will eventually do the corresponding heap_close(),
+	 * but *not* release the lock.
+	 */
+	pstate->p_target_relation = parserOpenTable(pstate, relation,
+												RowExclusiveLock);
+
+	
+}
+
+
 /*
  * Simplify InhOption (yes/no/default) into boolean yes/no.
  *
diff --git a/src/backend/rewrite/rewriteHandler.c b/src/backend/rewrite/rewriteHandler.c
index 25b44dd..9e3b30b 100644
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -1837,6 +1837,45 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 }
 
 
+#define insert_rewrite (1<<0) /*insert merge action has already been processed by rewriter*/
+#define delete_rewrite (1<<1) 
+#define update_rewrite (1<<2)
+
+#define	insert_instead (1<<3) /*insert merge action is fully replace by rules.*/
+#define delete_instead (1<<4)
+#define update_instead (1<<5)
+
+
+#define merge_action_already_rewrite(acttype, flag) \
+	((acttype == CMD_INSERT && (flag & insert_rewrite)) || \
+		(acttype == CMD_UPDATE && (flag & update_rewrite)) || \
+		(acttype == CMD_DELETE && (flag & delete_rewrite)))
+
+
+#define set_action_rewrite(acttype, flag)	\
+				if(acttype == CMD_INSERT)  \
+					{flag |= insert_rewrite;}\
+				else if(acttype == CMD_UPDATE)  \
+					{flag |= update_rewrite;}\
+				else if(acttype == CMD_DELETE)  \
+					{flag |= delete_rewrite;}
+
+
+				
+#define merge_action_instead(acttype, flag)		\
+			((acttype == CMD_INSERT && (flag & insert_instead)) || \
+				(acttype == CMD_UPDATE && (flag & update_instead)) || \
+				(acttype == CMD_DELETE && (flag & delete_instead)))
+
+#define set_action_instead(acttype, flag)\
+				if(acttype == CMD_INSERT)  \
+					{flag |= insert_instead;}\
+				else if(acttype == CMD_UPDATE)  \
+					{flag |= update_instead;}\
+				else if(acttype == CMD_DELETE)  \
+					{flag |= delete_instead;}
+
+
 /*
  * QueryRewrite -
  *	  Primary entry point to the query rewriter.
@@ -1861,7 +1900,149 @@ QueryRewrite(Query *parsetree)
 	 *
 	 * Apply all non-SELECT rules possibly getting 0 or many queries
 	 */
-	querylist = RewriteQuery(parsetree, NIL);
+
+	
+	if(parsetree->commandType == CMD_MERGE)
+	{
+		/*
+		*for merge query, we have a set of action queries (not subquery).
+		*each of these action queries should be applied to RewriteQuery(). 
+		*/
+		ListCell   *cell,
+				   *prev,
+				   *next;
+
+		int flag = 0;
+
+		
+		List *pre_qry = NIL;
+		List *post_qry = NIL;
+
+
+		querylist = NIL;
+		
+
+		/*rewrite the merge action queries one by one.*/
+		prev = NULL;
+
+		for (cell = list_head(parsetree->mergeActQry); cell; cell = next)
+		{
+			List *queryList4action = NIL;
+			Query *actionqry;
+			Query *q;
+
+			
+			actionqry = lfirst(cell);
+
+			next = lnext(cell);
+
+			/*if this kind of actions are fully replaced by rules, we delete it from the action list*/	
+			if(merge_action_instead(actionqry->commandType, flag))
+			{
+				parsetree->mergeActQry = list_delete_cell(parsetree->mergeActQry, cell, prev);
+				continue;
+			}
+
+
+			/*if this kind of actions are already processed by rewriter, skip it.*/
+			if(merge_action_already_rewrite(actionqry->commandType, flag))
+			{
+				/*	Still need to call RewriteQuery(), since we need the process on target list and so on. 
+					BUT, the returned list is discarded
+				*/
+				RewriteQuery(actionqry, NIL);
+			
+				prev = cell; 
+				continue;
+			}
+
+			/*ok this action has not been processed before, let's do it now.*/
+			queryList4action = RewriteQuery(actionqry, NIL);
+
+			/*this kind of actions has been processed.*/
+			set_action_rewrite(actionqry->commandType,flag); 
+
+			/*if the returning list is nil, this merge action is replaced by a do-nothing rule*/
+			if(queryList4action == NIL) 
+			{
+				/*set the flag for other merge actions of the same type*/
+				set_action_instead(actionqry->commandType, flag);
+
+				/*delete the action.*/
+				parsetree->mergeActQry = list_delete_cell(parsetree->mergeActQry, cell, prev);
+
+				continue;
+			}
+
+			
+			/*the merge action query could be one of the elements in the rewriten list. 
+			*if it is in the list, it must be the head or tail.
+			*/
+			q = (Query *)linitial(queryList4action);
+			if(q->querySource == QSRC_ORIGINAL)
+			{
+				/*
+				*the merge action is the head, the remaining part of the list are the queries generated by rules
+				*we put them in the post_qry list. 
+				*/
+				if(querylist == NIL)
+					querylist = list_make1(parsetree);
+
+
+				queryList4action = list_delete_first(queryList4action);
+				post_qry = list_concat(post_qry,queryList4action);
+				prev = cell; 
+				continue;
+
+			}
+			
+			
+			q = (Query *)llast(queryList4action);
+			if(q->querySource == QSRC_ORIGINAL)
+			{
+				/*the merge action is the tail. Put the rule queries in pre_qry list*/
+
+				if(querylist == NIL)
+					querylist = list_make1(parsetree);
+					
+				queryList4action = list_truncate(queryList4action,list_length(queryList4action)-1);
+
+				pre_qry = list_concat(pre_qry,queryList4action);
+
+				prev = cell; 
+				continue;
+
+			}	
+				
+
+			/*here, the merge action query is not in the rewriten query list, 
+			*which means the action should be deleted.
+			*It is replaced by INSTEAD rule(s). We need to delete the action  
+
+				For a INSERT action, we put the rule queries in the post list
+				otherwise, in the pre list
+			*/
+			if(actionqry->commandType == CMD_INSERT)
+				post_qry = list_concat(post_qry,queryList4action);
+			else
+				pre_qry = list_concat(pre_qry,queryList4action);
+			
+			set_action_instead(actionqry->commandType, flag);
+			parsetree->mergeActQry = list_delete_cell(parsetree->mergeActQry, cell, prev);
+		}				
+
+		
+
+		/*finally, put the 3 lists into one. 
+		*If all the merge actions are replaced by rules, the original merge query 
+		*will not be involved in the querylist.
+		*/
+		querylist = list_concat(pre_qry,querylist);
+		querylist = list_concat(querylist, post_qry);
+			
+	}
+	else
+		querylist = RewriteQuery(parsetree, NIL);
 
 	/*
 	 * Step 2
diff --git a/src/backend/tcop/pquery.c b/src/backend/tcop/pquery.c
index 8ad4915..0dc3117 100644
--- a/src/backend/tcop/pquery.c
+++ b/src/backend/tcop/pquery.c
@@ -225,6 +225,10 @@ ProcessQuery(PlannedStmt *plan,
 				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
 						 "DELETE %u", queryDesc->estate->es_processed);
 				break;
+			case CMD_MERGE:
+				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
+						 "MERGE %u", queryDesc->estate->es_processed);
+				break;
 			default:
 				strcpy(completionTag, "???");
 				break;
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 8960246..2733e5d 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -125,6 +125,7 @@ CommandIsReadOnly(Node *parsetree)
 			case CMD_UPDATE:
 			case CMD_INSERT:
 			case CMD_DELETE:
+			case CMD_MERGE:
 				return false;
 			default:
 				elog(WARNING, "unrecognized commandType: %d",
@@ -1398,6 +1399,10 @@ CreateCommandTag(Node *parsetree)
 			tag = "SELECT";
 			break;
 
+		case T_MergeStmt:
+			tag = "MERGE";
+			break;
+		
 			/* utility statements --- same whether raw or cooked */
 		case T_TransactionStmt:
 			{
@@ -2235,6 +2240,7 @@ GetCommandLogLevel(Node *parsetree)
 		case T_InsertStmt:
 		case T_DeleteStmt:
 		case T_UpdateStmt:
+		case T_MergeStmt:
 			lev = LOGSTMT_MOD;
 			break;
 
diff --git a/src/include/executor/nodeModifyTable.h b/src/include/executor/nodeModifyTable.h
index 67ba3e8..92f50ed 100644
--- a/src/include/executor/nodeModifyTable.h
+++ b/src/include/executor/nodeModifyTable.h
@@ -16,6 +16,9 @@
 #include "nodes/execnodes.h"
 
 extern ModifyTableState *ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags);
+
+extern MergeActionState *ExecInitMergeAction(MergeAction *node, EState *estate, int eflags);
+
 extern TupleTableSlot *ExecModifyTable(ModifyTableState *node);
 extern void ExecEndModifyTable(ModifyTableState *node);
 extern void ExecReScanModifyTable(ModifyTableState *node);
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 09fdb5d..cfd09e6 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1031,9 +1031,22 @@ typedef struct ModifyTableState
 	int			mt_whichplan;	/* which one is being executed (0..n-1) */
 	EPQState	mt_epqstate;	/* for evaluating EvalPlanQual rechecks */
 	bool		fireBSTriggers; /* do we need to fire stmt triggers? */
+	List 		*mergeActPstates; /*the list of the planstate of meger command actions. 
+									NIL if this is not a merge command.
+									The elements if it are MergeActionState nodes*/
 } ModifyTableState;
 
 /* ----------------
+ *	 MergeActionState information
+ * ----------------
+ */
+typedef struct MergeActionState
+{
+	PlanState	ps;				/* its first field is NodeTag */
+	CmdType		operation;	
+} MergeActionState;
+
+/* ----------------
  *	 AppendState information
  *
  *		nplans			how many plans are in the array
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index a5f5df5..053eee7 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -44,6 +44,7 @@ typedef enum NodeTag
 	T_Plan = 100,
 	T_Result,
 	T_ModifyTable,
+	T_MergeAction,
 	T_Append,
 	T_RecursiveUnion,
 	T_BitmapAnd,
@@ -86,6 +87,7 @@ typedef enum NodeTag
 	T_PlanState = 200,
 	T_ResultState,
 	T_ModifyTableState,
+	T_MergeActionState,
 	T_AppendState,
 	T_RecursiveUnionState,
 	T_BitmapAndState,
@@ -347,6 +349,14 @@ typedef enum NodeTag
 	T_AlterUserMappingStmt,
 	T_DropUserMappingStmt,
 	T_AlterTableSpaceOptionsStmt,
+		
+	T_MergeStmt,
+	T_MergeConditionAction,
+	T_MergeUpdate, 
+	T_MergeDelete,	
+	T_MergeInsert,
+		
+		
 
 	/*
 	 * TAGS FOR PARSE TREE NODES (parsenodes.h)
@@ -511,6 +521,7 @@ typedef enum CmdType
 	CMD_UPDATE,					/* update stmt */
 	CMD_INSERT,					/* insert stmt */
 	CMD_DELETE,
+	CMD_MERGE,						/*merge stmt*/
 	CMD_UTILITY,				/* cmds like create, destroy, copy, vacuum,
 								 * etc. */
 	CMD_NOTHING					/* dummy command for instead nothing rules
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index b591073..8638a42 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -146,6 +146,11 @@ typedef struct Query
 
 	Node	   *setOperations;	/* set-operation tree if this is top level of
 								 * a UNION/INTERSECT/EXCEPT query */
+
+	bool		 isMergeAction; /*if this query is a merge action. */	 
+
+	List 		*mergeActQry; /* the list of all the merge actions. 
+								* used only for merge query statment*/							 
 } Query;
 
 
@@ -990,6 +995,44 @@ typedef struct SelectStmt
 	/* Eventually add fields for CORRESPONDING spec here */
 } SelectStmt;
 
+/*The structure for MERGE command statement*/
+typedef struct MergeStmt
+{
+	NodeTag		type;
+	RangeVar   	*relation;		/*targe relation for merge */
+
+	/* source relations for the merge. 
+	*Currently, we only allwo single-source merge, 
+	*so the length of this list should always be 1 
+	*/
+	List		*source;		
+	Node	   	*matchCondition;	/* qualifications of the merge*/
+
+	/*list  of MergeConditionAction structure. 
+	*It stores all the matched / not-matched conditions and the corresponding actions
+	*The elments of this list are MergeConditionAction nodes
+	*/
+	List	   	*actions;		
+
+}MergeStmt;
+
+/*	the structure for the actions of MERGE command. 
+*	Holds info of the clauses like "... WHEN MATCHED AND ... THEN UPDATE/DELETE/INSERT"
+*/
+typedef struct MergeConditionAction
+{
+	NodeTag		type;
+	bool 		match; /*match or not match*/
+	Node		*condition;/*the AND condition for this action*/
+	Node 		*action; /*the actions: delete , insert or update*/
+}MergeConditionAction;
+
+/*
+*	The merge action nodes are in fact the ordinary nodes of UPDATE,DELETE and INSERT
+*/
+typedef UpdateStmt MergeUpdate;
+typedef DeleteStmt MergeDelete;
+typedef InsertStmt MergeInsert;
 
 /* ----------------------
  *		Set Operation node for post-analysis query trees
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 037bc0b..5a73d60 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -169,9 +169,22 @@ typedef struct ModifyTable
 	List	   *returningLists; /* per-target-table RETURNING tlists */
 	List	   *rowMarks;		/* PlanRowMarks (non-locking only) */
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
+	List 		*mergeActPlan;	/*the plans for merge actions, which are also ModifyTable nodes*/
 } ModifyTable;
 
 /* ----------------
+ *	 MergeAction node -
+ *		The plan node for the actions of MERGE command
+ * ----------------
+ */
+typedef struct MergeAction
+{
+	Plan plan;
+	CmdType	operation;/* INSERT, UPDATE, or DELETE */
+	List *flattenedqual; /*the flattened qual expression of action*/
+}MergeAction;
+
+/* ----------------
  *	 Append node -
  *		Generate the concatenation of the results of sub-plans.
  * ----------------
diff --git a/src/include/optimizer/planner.h b/src/include/optimizer/planner.h
index 805dee7..6d7ff4f 100644
--- a/src/include/optimizer/planner.h
+++ b/src/include/optimizer/planner.h
@@ -34,6 +34,7 @@ extern Plan *subquery_planner(PlannerGlobal *glob, Query *parse,
 				 PlannerInfo *parent_root,
 				 bool hasRecursion, double tuple_fraction,
 				 PlannerInfo **subroot);
+extern ModifyTable *merge_action_planner(PlannerGlobal *glob, Query *parse, Plan *top_plan);
 
 extern Expr *expression_planner(Expr *expr);
 
diff --git a/src/include/optimizer/var.h b/src/include/optimizer/var.h
index b0e04a0..4d6c9e8 100644
--- a/src/include/optimizer/var.h
+++ b/src/include/optimizer/var.h
@@ -15,6 +15,7 @@
 #define VAR_H
 
 #include "nodes/relation.h"
+#include "nodes/plannodes.h"
 
 typedef enum
 {
@@ -32,5 +33,5 @@ extern int	locate_var_of_relation(Node *node, int relid, int levelsup);
 extern int	find_minimum_var_level(Node *node);
 extern List *pull_var_clause(Node *node, PVCPlaceHolderBehavior behavior);
 extern Node *flatten_join_alias_vars(PlannerInfo *root, Node *node);
-
+extern void push_up_merge_action_vars(MergeAction * actplan,Query * actqry);
 #endif   /* VAR_H */
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 49d4b6c..436d459 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -229,7 +229,9 @@ PG_KEYWORD("lock", LOCK_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("login", LOGIN_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("mapping", MAPPING, UNRESERVED_KEYWORD)
 PG_KEYWORD("match", MATCH, UNRESERVED_KEYWORD)
+PG_KEYWORD("matched", MATCHED, UNRESERVED_KEYWORD)
 PG_KEYWORD("maxvalue", MAXVALUE, UNRESERVED_KEYWORD)
+PG_KEYWORD("merge", MERGE, UNRESERVED_KEYWORD)
 PG_KEYWORD("minute", MINUTE_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("minvalue", MINVALUE, UNRESERVED_KEYWORD)
 PG_KEYWORD("mode", MODE, UNRESERVED_KEYWORD)
diff --git a/src/include/parser/parse_clause.h b/src/include/parser/parse_clause.h
index f3d3ee9..e4312d8 100644
--- a/src/include/parser/parse_clause.h
+++ b/src/include/parser/parse_clause.h
@@ -19,6 +19,8 @@
 extern void transformFromClause(ParseState *pstate, List *frmList);
 extern int setTargetTable(ParseState *pstate, RangeVar *relation,
 			   bool inh, bool alsoSource, AclMode requiredPerms);
+extern void setTargetTableLock(ParseState *pstate, RangeVar *relation);
+
 extern bool interpretInhOption(InhOption inhOpt);
 extern bool interpretOidsOption(List *defList);
 

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index b776ad1..cdb492b 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -73,6 +73,8 @@ static void show_sort_keys(SortState *sortstate, List *ancestors,
 static void show_sort_info(SortState *sortstate, ExplainState *es);
 static void show_hash_info(HashState *hashstate, ExplainState *es);
 static const char *explain_get_index_name(Oid indexId);
+static void ExplainMergeActions(ModifyTableState *mt_planstate, 
+									List *ancestors, ExplainState *es);
 static void ExplainScanTarget(Scan *plan, ExplainState *es);
 static void ExplainMemberNodes(List *plans, PlanState **planstates,
 				   List *ancestors, ExplainState *es);
@@ -636,6 +638,9 @@ ExplainNode(PlanState *planstate, List *ancestors,
 				case CMD_DELETE:
 					pname = operation = "Delete";
 					break;
+				case CMD_MERGE:
+					pname = operation = "Merge";
+					break;
 				default:
 					pname = "???";
 					break;
@@ -1190,6 +1195,8 @@ ExplainNode(PlanState *planstate, List *ancestors,
 	switch (nodeTag(plan))
 	{
 		case T_ModifyTable:
+			ExplainMergeActions((ModifyTableState *)planstate, ancestors, es);
+			
 			ExplainMemberNodes(((ModifyTable *) plan)->plans,
 							   ((ModifyTableState *) planstate)->mt_plans,
 							   ancestors, es);
@@ -1482,6 +1489,55 @@ explain_get_index_name(Oid indexId)
 	return result;
 }
 
+static void
+ExplainMergeActions(ModifyTableState *mt_planstate, List *ancestors, ExplainState *es)
+{
+	ListCell *l;
+	
+	if(mt_planstate->operation != CMD_MERGE || mt_planstate->mergeActPstates == NIL)
+		return;
+
+	foreach(l,mt_planstate->mergeActPstates)
+	{
+		ModifyTableState *mt_state = (ModifyTableState *)lfirst(l);
+
+		MergeActionState *act_pstate = (MergeActionState *)mt_state->mt_plans[0];
+
+		MergeAction *act_plan = (MergeAction *)act_pstate->ps.plan;
+
+		switch(act_pstate->operation)
+		{
+			case CMD_INSERT:
+				if(act_plan->flattenedqual)
+					ExplainPropertyText("Action", "Insert When Not Matched And",es);
+				else
+					ExplainPropertyText("Action", "Insert When Not Matched",es);				
+				break;
+			case CMD_UPDATE:
+				if(act_plan->flattenedqual)
+					ExplainPropertyText("Action", "Update When Matched And",es);
+				else
+					ExplainPropertyText("Action", "Update When Matched",es);	
+				break;
+			case CMD_DELETE:
+				if(act_plan->flattenedqual)
+					ExplainPropertyText("Action", "Delete When Matched And",es);
+				else
+					ExplainPropertyText("Action", "Delete When Matched",es);	
+				break;	
+			default:
+				elog(ERROR, "unknown merge action type");
+		}
+
+		/*
+		*	We need a faltened qual expression for show_qual
+		*/
+		show_qual(act_plan->flattenedqual, "  qual", &act_pstate->ps, ancestors, true, es);
+	}
+	
+}
+
+
 /*
  * Show the target of a Scan node
  */
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 8cd3ae9..9a2db5f 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -170,6 +170,7 @@ standard_ExecutorStart(QueryDesc *queryDesc, int eflags)
 		case CMD_INSERT:
 		case CMD_DELETE:
 		case CMD_UPDATE:
+		case CMD_MERGE:	
 			estate->es_output_cid = GetCurrentCommandId(true);
 			break;
 
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index f4cc7d9..2d1a4e7 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -153,6 +153,11 @@ ExecInitNode(Plan *node, EState *estate, int eflags)
 													   estate, eflags);
 			break;
 
+		case T_MergeAction:
+			result = (PlanState *) ExecInitMergeAction((MergeAction*) node,
+													   estate, eflags);
+			break;
+			
 		case T_Append:
 			result = (PlanState *) ExecInitAppend((Append *) node,
 												  estate, eflags);
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 8619ce3..bd84784 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -583,6 +583,116 @@ lreplace:;
 }
 
 
+static TupleTableSlot *
+ExecMerge(ItemPointer tupleid,
+		   TupleTableSlot *slot,
+		   TupleTableSlot *planSlot,
+		   ModifyTableState *node,
+		   EState *estate)
+{
+
+	TupleTableSlot *actslot = NULL;
+	TupleTableSlot *res = NULL;
+	ListCell *each;
+
+	/*
+	*	try the merge actions one by one
+	*/
+	foreach(each, node->mergeActPstates)
+	{
+		ModifyTableState *mt_pstate;
+
+		MergeActionState *action_pstate; 
+
+		ExprContext *econtext;
+
+		
+		mt_pstate = (ModifyTableState *)lfirst(each);
+
+		/*
+		*	mt_pstate is supposed to have only ONE mt_plans, 
+		*	which is a MergeActionState
+		*/
+		Assert(mt_pstate->mt_nplans == 1);
+
+		action_pstate = (MergeActionState *)mt_pstate->mt_plans[0];
+
+		/*
+		*	If tupleid == NULL, it is a NOT MATCHED case, in which we can only do INSERT action
+		*	If tupleid != NULL, it is a MATCHED case, in which we can only do UPDATE or DELETE action
+		*/		
+		if((tupleid == NULL && action_pstate->operation != CMD_INSERT) ||
+			(tupleid != NULL && action_pstate->operation == CMD_INSERT))
+		{
+			continue;
+		}
+
+		/*
+		*	Setup the expression context
+		*/
+		econtext = action_pstate->ps.ps_ExprContext;
+
+		/*
+		If the action has an additional qual, which is not satisfied, skip it
+		*/	
+		
+		if(action_pstate->ps.qual) 
+		{	
+			ResetExprContext(econtext);
+		
+			econtext->ecxt_scantuple = slot;
+			econtext->ecxt_outertuple = planSlot;
+
+			if(!ExecQual(action_pstate->ps.qual, econtext,false))
+			{	
+				continue;
+			}
+		}
+		/*
+		*	Now we start to exec this action. Firstly , project the result tuple slot. 
+		*	The merge action result slot is projected in the same way as a returning slot. 
+		*	so we call ExecProcessReturning() directly here.
+		*/
+		if(action_pstate->operation != CMD_DELETE)
+			actslot = ExecProcessReturning(action_pstate->ps.ps_ProjInfo, slot, planSlot);
+
+		switch (action_pstate->operation)
+		{
+			case CMD_INSERT:
+				res = ExecInsert(actslot, planSlot, estate);
+				break;
+			case CMD_UPDATE:
+				res = ExecUpdate(tupleid,
+							actslot,
+							planSlot,
+							&mt_pstate->mt_epqstate,
+							estate);
+				break;
+			case CMD_DELETE:
+				res = ExecDelete(tupleid, 
+							planSlot, 
+							&mt_pstate->mt_epqstate,
+							estate);
+				break;
+			default:
+				elog(ERROR, "unknown merge action type");
+				break;
+		}
+
+
+		/*
+		* The current action is executed, no need to do the remain actions
+		*/	
+		return res;
+	}
+
+	/*
+	* Here, no action is taken. Let's pass this slot
+	*/	
+	return NULL;
+	
+}
+
 /*
  * Process BEFORE EACH STATEMENT triggers
  */
@@ -603,6 +713,9 @@ fireBSTriggers(ModifyTableState *node)
 			ExecBSDeleteTriggers(node->ps.state,
 								 node->ps.state->es_result_relations);
 			break;
+		case CMD_MERGE:
+			printf("not sure about the BS triggers of merge\n");
+			break;
 		default:
 			elog(ERROR, "unknown operation");
 			break;
@@ -629,6 +742,9 @@ fireASTriggers(ModifyTableState *node)
 			ExecASDeleteTriggers(node->ps.state,
 								 node->ps.state->es_result_relations);
 			break;
+		case CMD_MERGE:
+			printf("not sure about the AS triggers of merge\n");
+			break;	
 		default:
 			elog(ERROR, "unknown operation");
 			break;
@@ -708,20 +824,34 @@ ExecModifyTable(ModifyTableState *node)
 			/*
 			 * extract the 'ctid' junk attribute.
 			 */
-			if (operation == CMD_UPDATE || operation == CMD_DELETE)
+			if (operation == CMD_UPDATE || operation == CMD_DELETE || operation == CMD_MERGE)
 			{
 				Datum		datum;
 				bool		isNull;
 
 				datum = ExecGetJunkAttribute(slot, junkfilter->jf_junkAttNo,
 											 &isNull);
-				/* shouldn't ever get a null result... */
+				
 				if (isNull)
-					elog(ERROR, "ctid is NULL");
-
-				tupleid = (ItemPointer) DatumGetPointer(datum);
-				tuple_ctid = *tupleid;	/* be sure we don't free the ctid!! */
-				tupleid = &tuple_ctid;
+				{
+					/*
+					*	shouldn't ever get a null result for update and delete. 
+					*	Merge command will get a null ctid in "NOT MATCHED" case
+					*/
+					if(operation != CMD_MERGE)
+						elog(ERROR, "ctid is NULL");
+					else
+						tupleid = NULL;
+				}	
+				else
+				{
+				
+					tupleid = (ItemPointer) DatumGetPointer(datum);
+					
+					tuple_ctid = *tupleid;	/* be sure we don't free the ctid!! */
+					tupleid = &tuple_ctid;
+					
+				}
 			}
 
 			/*
@@ -744,6 +874,11 @@ ExecModifyTable(ModifyTableState *node)
 				slot = ExecDelete(tupleid, planSlot,
 								  &node->mt_epqstate, estate);
 				break;
+			case CMD_MERGE:
+				slot = ExecMerge(tupleid, slot, planSlot,
+								  node, estate);
+				break;	
+				
 			default:
 				elog(ERROR, "unknown operation");
 				break;
@@ -771,6 +906,86 @@ ExecModifyTable(ModifyTableState *node)
 	return NULL;
 }
 
+
+/*
+*	When init a merge plan, we also need init its action plans. 
+*	These action plans are "MergeAction" plans (new plan node for the merge actions).
+*	
+*	In this function, we only want to handle the tlist and qual in the plan.
+*	The returning result is a  "MergeActionState".  
+*/
+MergeActionState *
+ExecInitMergeAction(MergeAction *node, EState *estate, int eflags)
+{
+	MergeActionState *result;
+	
+	/*
+	 * do nothing when we get to the end of a leaf on tree.
+	 */
+	if (node == NULL)
+		return NULL;
+
+		
+	/*
+	 * create state structure
+	 */
+	result = makeNode(MergeActionState);
+	result->operation = node->operation;
+	result->ps.plan = (Plan *)node;
+	result->ps.state = estate;
+
+	/*
+	 * tuple table initialization
+	 */
+	ExecInitResultTupleSlot(estate, &result->ps);
+
+
+	
+	/*
+	 * initialize tuple type 
+	 */
+	ExecAssignResultTypeFromTL(&result->ps);
+
+		
+	/*
+	 * create expression context for node
+	 */
+	 
+	ExecAssignExprContext(estate, &result->ps);
+
+
+	/*
+	 * initialize child expressions
+	 */
+	result->ps.targetlist = (List *)
+		ExecInitExpr((Expr *) node->plan.targetlist,  &result->ps);
+
+	
+	result->ps.qual = (List *)
+		ExecInitExpr((Expr *) node->plan.qual, &result->ps);
+
+	
+	/*
+	* init the projection information
+	*/
+	ExecAssignProjectionInfo(&result->ps, NULL);
+
+	/*
+	do we need a check for the plan output here ?
+	
+	if(estate->es_result_relation_info == NULL)
+		printf("re infro is null\n");
+
+	if(estate->es_result_relation_info->ri_RelationDesc == NULL)
+		printf("r relation desc is nUll\n");
+		ExecCheckPlanOutput(estate->es_result_relation_info->ri_RelationDesc,
+								node->targetlist);
+	printf("finish check plan output for merge actio \n");	
+	*/
+	return result;
+}
+
+
 /* ----------------------------------------------------------------
  *		ExecInitModifyTable
  * ----------------------------------------------------------------
@@ -786,6 +1001,7 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	Plan	   *subplan;
 	ListCell   *l;
 	int			i;
+	bool 		isMergeAction = false;
 
 	/* check for unsupported flags */
 	Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
@@ -826,6 +1042,16 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	foreach(l, node->plans)
 	{
 		subplan = (Plan *) lfirst(l);
+
+		/*
+		* 	test if this subplan node is a MergeAction. 
+		* 	We need this information for setting the junckfilter. 
+		*	juckfiler is necessary for an ordinary UPDATE/DELETE plan, 
+		*	but not for an UPDATE/DELETE merge action  
+		*/		
+		if(IsA(subplan, MergeAction))
+			isMergeAction = true;
+		
 		mtstate->mt_plans[i] = ExecInitNode(subplan, estate, eflags);
 		estate->es_result_relation_info++;
 		i++;
@@ -955,7 +1181,9 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 				break;
 			case CMD_UPDATE:
 			case CMD_DELETE:
-				junk_filter_needed = true;
+			case CMD_MERGE:	
+				if(!isMergeAction)
+					junk_filter_needed = true;
 				break;
 			default:
 				elog(ERROR, "unknown operation");
@@ -978,9 +1206,9 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 							resultRelInfo->ri_RelationDesc->rd_att->tdhasoid,
 									   ExecInitExtraTupleSlot(estate));
 
-				if (operation == CMD_UPDATE || operation == CMD_DELETE)
+				if (operation == CMD_UPDATE || operation == CMD_DELETE || operation == CMD_MERGE)
 				{
-					/* For UPDATE/DELETE, find the ctid junk attr now */
+					/* For UPDATE/DELETE/MERGE, find the ctid junk attr now */
 					j->jf_junkAttNo = ExecFindJunkAttribute(j, "ctid");
 					if (!AttributeNumberIsValid(j->jf_junkAttNo))
 						elog(ERROR, "could not find junk ctid column");
@@ -1006,6 +1234,21 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 	if (estate->es_trig_tuple_slot == NULL)
 		estate->es_trig_tuple_slot = ExecInitExtraTupleSlot(estate);
 
+	
+	/*
+	* for the merge actions, we need to similar things as above
+	*/
+
+	foreach(l, node->mergeActPlan)
+	{
+		PlanState *actpstate = ExecInitNode((Plan *)lfirst(l),  estate, 0);
+		/*
+		* put the pstates of each action into ModifyTableState
+		*/
+		mtstate->mergeActPstates = lappend(mtstate->mergeActPstates, actpstate);
+		
+	}
+	
 	return mtstate;
 }
 
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 9af1217..c12e7d8 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -176,6 +176,7 @@ _copyModifyTable(ModifyTable *from)
 	COPY_NODE_FIELD(returningLists);
 	COPY_NODE_FIELD(rowMarks);
 	COPY_SCALAR_FIELD(epqParam);
+	COPY_NODE_FIELD(mergeActPlan);
 
 	return newnode;
 }
@@ -2273,6 +2274,10 @@ _copyQuery(Query *from)
 	COPY_NODE_FIELD(rowMarks);
 	COPY_NODE_FIELD(setOperations);
 
+	COPY_SCALAR_FIELD(isMergeAction);
+	/*merge action list*/
+	COPY_NODE_FIELD(mergeActQry); 
+
 	return newnode;
 }
 
@@ -2343,6 +2348,64 @@ _copySelectStmt(SelectStmt *from)
 	return newnode;
 }
 
+
+static MergeStmt *
+_copyMergeStmt(MergeStmt *from)
+{
+	MergeStmt *newnode = makeNode(MergeStmt);
+
+	COPY_NODE_FIELD(relation);
+	COPY_NODE_FIELD(source);
+	COPY_NODE_FIELD(matchCondition);
+	COPY_NODE_FIELD(actions);
+	
+	return newnode;
+	
+}
+
+
+static MergeConditionAction *
+_copyMergeConditionAction(MergeConditionAction *from)
+{
+	MergeConditionAction *newnode = makeNode(MergeConditionAction);
+
+	COPY_SCALAR_FIELD(match);
+	COPY_NODE_FIELD(condition);
+	COPY_NODE_FIELD(action);
+
+	return newnode;
+}
+
+static MergeUpdate *
+_copyMergeUpdate(MergeUpdate *from)
+{
+	MergeUpdate *newNode = (MergeUpdate *)_copyUpdateStmt((UpdateStmt *) from);
+	newNode->type = T_MergeUpdate;
+
+	return newNode;
+}
+
+static MergeInsert *
+_copyMergeInsert(MergeInsert *from)
+{
+	MergeInsert *newNode = (MergeInsert *)_copyInsertStmt((InsertStmt *) from);
+	newNode->type = T_MergeInsert;
+
+	return newNode;
+}
+
+
+static MergeDelete *
+_copyMergeDelete(MergeDelete *from)
+{
+	MergeDelete *newNode = (MergeDelete *)_copyDeleteStmt((DeleteStmt *) from);
+	newNode->type = T_MergeDelete;
+
+	return newNode;
+}
+
+
+
 static SetOperationStmt *
 _copySetOperationStmt(SetOperationStmt *from)
 {
@@ -3904,6 +3967,21 @@ copyObject(void *from)
 		case T_SelectStmt:
 			retval = _copySelectStmt(from);
 			break;
+		case T_MergeStmt:
+			retval = _copyMergeStmt(from);
+			break;
+		case T_MergeConditionAction:
+			retval = _copyMergeConditionAction(from);
+			break;
+		case T_MergeUpdate:
+			retval = _copyMergeUpdate(from);
+			break;
+		case T_MergeInsert:
+			retval = _copyMergeInsert(from);
+			break;
+		case T_MergeDelete:
+			retval = _copyMergeDelete(from);
+			break;
 		case T_SetOperationStmt:
 			retval = _copySetOperationStmt(from);
 			break;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 70b3c62..cd7ee2b 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -878,6 +878,7 @@ _equalQuery(Query *a, Query *b)
 	COMPARE_NODE_FIELD(rowMarks);
 	COMPARE_NODE_FIELD(setOperations);
 
+	COMPARE_SCALAR_FIELD(isMergeAction);
 	return true;
 }
 
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 0454aa5..f9690a4 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -331,6 +331,7 @@ _outModifyTable(StringInfo str, ModifyTable *node)
 	WRITE_NODE_FIELD(returningLists);
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_INT_FIELD(epqParam);
+	WRITE_NODE_FIELD(mergeActPlan);
 }
 
 static void
@@ -2020,8 +2021,60 @@ _outQuery(StringInfo str, Query *node)
 	WRITE_NODE_FIELD(limitCount);
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_NODE_FIELD(setOperations);
+	WRITE_BOOL_FIELD(isMergeAction);
+	WRITE_NODE_FIELD(mergeActQry);
 }
 
+
+static void
+_outMergeConditionAction(StringInfo str, MergeConditionAction *node)
+{
+	WRITE_NODE_TYPE("MERGECONDITIONACTION");
+
+	WRITE_BOOL_FIELD(match);
+	
+	WRITE_NODE_FIELD(condition);
+	WRITE_NODE_FIELD(action);
+
+
+}
+
+static void
+_outMergeStmt(StringInfo str, MergeStmt *node)
+{
+	WRITE_NODE_TYPE("MERGESTMT");
+
+	WRITE_NODE_FIELD(relation);
+	WRITE_NODE_FIELD(source);
+	WRITE_NODE_FIELD(matchCondition);
+	WRITE_NODE_FIELD(actions);
+
+}
+
+static void
+_outMergeAction(StringInfo str, MergeAction*node)
+{
+	_outPlanInfo(str, (Plan *)node);
+
+	WRITE_ENUM_FIELD(operation, CmdType);
+
+}
+
+static void 
+_outDeleteStmt(StringInfo str, DeleteStmt *node)
+{
+	WRITE_NODE_TYPE("DELETESTMT");
+
+	WRITE_NODE_FIELD(relation);
+	WRITE_NODE_FIELD(usingClause);
+	WRITE_NODE_FIELD(whereClause);
+	WRITE_NODE_FIELD(returningList);
+
+
+}
+
+
+
 static void
 _outSortGroupClause(StringInfo str, SortGroupClause *node)
 {
@@ -2905,6 +2958,19 @@ _outNode(StringInfo str, void *obj)
 			case T_XmlSerialize:
 				_outXmlSerialize(str, obj);
 				break;
+			case T_MergeAction:
+				_outMergeAction(str, obj);
+				break;
+			case T_MergeStmt:
+				_outMergeStmt(str, obj);
+				break;
+			case T_MergeConditionAction:
+				_outMergeConditionAction(str,obj);
+				break;
+			case T_DeleteStmt:
+				_outDeleteStmt(str,obj);
+				break;
+					
 
 			default:
 
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index bc6e2a6..b792132 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -218,7 +218,9 @@ _readQuery(void)
 	READ_NODE_FIELD(limitCount);
 	READ_NODE_FIELD(rowMarks);
 	READ_NODE_FIELD(setOperations);
-
+	READ_BOOL_FIELD(isMergeAction);
+	READ_NODE_FIELD(mergeActQry);
+	
 	READ_DONE();
 }
 
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 3950ab4..0057547 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -565,6 +565,26 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 											 returningLists,
 											 rowMarks,
 											 SS_assign_special_param(root));
+
+			/*do a simple plan for each actions in the merge command.
+			*put them in mergeActPlan list;
+			*/
+			if(parse->commandType == CMD_MERGE)
+			{
+				ListCell *l;
+				ModifyTable *top_plan = (ModifyTable *)plan;
+				foreach(l, parse->mergeActQry)
+				{
+					
+					Plan *actplan = (Plan *)merge_action_planner(glob, 
+																		(Query *)lfirst(l),
+																		(Plan *)linitial(top_plan->plans)
+																	);
+
+					top_plan->mergeActPlan = lappend(top_plan->mergeActPlan, actplan);
+				}
+
+			}
 		}
 	}
 
@@ -584,6 +604,109 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	return plan;
 }
 
+
+
+ModifyTable *
+merge_action_planner(PlannerGlobal *glob, Query *parse,
+				 Plan *top_plan)
+{
+	PlannerInfo *root;
+	MergeAction	*actplan;
+	ModifyTable *result;
+	
+	List	   	*returningLists;
+	List 		*rowMarks;
+
+	/*
+	 * no having clause in a merge action
+	 */
+	Assert(parse->havingQual == NULL);
+
+
+	/* Create a PlannerInfo data structure for this subquery */
+	root = makeNode(PlannerInfo);
+	root->parse = parse;
+	root->glob = glob;
+	root->query_level = 1;
+	root->parent_root = NULL;
+	root->planner_cxt = CurrentMemoryContext;
+	root->init_plans = NIL;
+	root->cte_plan_ids = NIL;
+	root->eq_classes = NIL;
+	root->append_rel_list = NIL;
+	root->hasPseudoConstantQuals = false;
+	root->hasRecursion = false;
+	root->wt_param_id = -1;
+	root->non_recursive_plan = NULL;
+
+
+	/*
+	*	Create the action plan node
+	*/
+	actplan = makeNode(MergeAction);
+	actplan->operation = parse->commandType;
+	
+	/*
+	 * Do expression preprocessing on targetlist and quals.
+	 */
+	parse->targetList = (List *)
+		preprocess_expression(root, (Node *) parse->targetList,
+							  EXPRKIND_TARGET);
+
+	preprocess_qual_conditions(root, (Node *) parse->jointree);
+	
+
+	/*
+	*	we need a flat qual for explaining
+	*/	
+	actplan->flattenedqual = flatten_join_alias_vars(root, parse->jointree->quals);
+	
+	/*copy the cost from the top_plan*/
+	actplan->plan.startup_cost = top_plan->startup_cost;
+	actplan->plan.total_cost = top_plan->total_cost;
+	actplan->plan.plan_rows = top_plan->plan_rows;
+	actplan->plan.plan_width = top_plan->plan_width;
+	
+	/*
+	*	prepare the result 
+	*/
+	actplan->plan.targetlist = preprocess_targetlist(root,parse->targetList);
+
+	actplan->plan.qual = (List *)parse->jointree->quals;
+	push_up_merge_action_vars(actplan, parse);
+
+	if (parse->returningList)
+	{
+		List	   *rlist;
+
+		Assert(parse->resultRelation);
+		rlist = set_returning_clause_references(root->glob,
+												parse->returningList,
+												&actplan->plan,
+											  parse->resultRelation);
+		returningLists = list_make1(rlist);
+	}
+	else
+		returningLists = NIL;
+
+
+	if (parse->rowMarks)
+		rowMarks = NIL;
+	else
+		rowMarks = root->rowMarks;
+	
+	result = make_modifytable(parse->commandType,
+										   copyObject(root->resultRelations),
+											 list_make1(actplan),
+											 returningLists,
+											 rowMarks,
+											 SS_assign_special_param(root));
+
+	
+	return result;
+}
+
+
 /*
  * preprocess_expression
  *		Do subquery_planner's preprocessing work for an expression,
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
index 59d3518..5685d52 100644
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -78,13 +78,20 @@ preprocess_targetlist(PlannerInfo *root, List *tlist)
 								  result_relation, range_table);
 
 	/*
-	 * for "update" and "delete" queries, add ctid of the result relation into
+	 * for "update" , "delete"  and "merge" queries, add ctid of the result relation into
 	 * the target list so that the ctid will propagate through execution and
 	 * ExecutePlan() will be able to identify the right tuple to replace or
 	 * delete.	This extra field is marked "junk" so that it is not stored
 	 * back into the tuple.
+	 *  
+	 * BUT, if the query node is a merge action, we don't need to expend the ctid attribute in tlist.
+	 * The tlist of the merge top level plan already contains a "ctid" junk attr of the target relation.
 	 */
-	if (command_type == CMD_UPDATE || command_type == CMD_DELETE)
+	 
+	if(!parse->isMergeAction  &&  
+			(command_type == CMD_UPDATE || 
+			command_type == CMD_DELETE || 
+			command_type == CMD_MERGE))
 	{
 		TargetEntry *tle;
 		Var		   *var;
diff --git a/src/backend/optimizer/util/var.c b/src/backend/optimizer/util/var.c
index 92c2208..f1fcbaa 100644
--- a/src/backend/optimizer/util/var.c
+++ b/src/backend/optimizer/util/var.c
@@ -67,6 +67,16 @@ typedef struct
 	bool		inserted_sublink;		/* have we inserted a SubLink? */
 } flatten_join_alias_vars_context;
 
+typedef struct
+{
+	int varno_source;
+	int varno_target;
+	int varno_join;
+
+	int offset_source;
+	int offset_target;
+} push_up_merge_action_vars_context;
+
 static bool pull_varnos_walker(Node *node,
 				   pull_varnos_context *context);
 static bool pull_varattnos_walker(Node *node, Bitmapset **varattnos);
@@ -83,6 +93,8 @@ static bool pull_var_clause_walker(Node *node,
 static Node *flatten_join_alias_vars_mutator(Node *node,
 								flatten_join_alias_vars_context *context);
 static Relids alias_relid_set(PlannerInfo *root, Relids relids);
+static bool push_up_merge_action_vars_walker(Node *node, 
+								push_up_merge_action_vars_context *context);
 
 
 /*
@@ -677,6 +689,88 @@ pull_var_clause_walker(Node *node, pull_var_clause_context *context)
 								  (void *) context);
 }
 
+/*
+*	When prepare for the MERGE command, we have made a left join between the 
+*	source table and target table as the main plan. In this case, the range table contains 
+*	ONLY THREE range table entries: 
+*	The first one is that of the source table, which may be a subquery or a plain table
+*	The second one is the entry of the targe table, which is a plain table
+*	The third one is a join expression with the sourse table and target table as its parameters.
+*
+*	Each merge action of the command has its own query and plan nodes as well. And, the vars 
+*	in its target list and qual expressions may refers to the attribute in any one of the above 3 
+* 	range table entries.
+*	
+*	However, since the result tuple slots of merge actions are projected from the returned tuple of
+*	the join, we need to mapping the vars of source table and target table to their corresponding 
+*	attributes in the third range table entry. 
+*
+*	This function does the opposit of the flatten_join_alias_vars() function. It walks through the 
+*	target list and qual of a MergeAction plan, changes the vars' varno and varattno to the 
+*	corresponding position in the upper level join RTE.
+*	
+*/
+void 
+push_up_merge_action_vars(MergeAction *actplan, Query *actqry)
+{
+	push_up_merge_action_vars_context context;
+	RangeTblEntry *source_rte = rt_fetch(1,actqry->rtable);
+
+
+	/*
+	* 	We are supposed to do a  more careful assingment of the values in context
+	*	But lets take a shortcut for simple.
+	*/
+	context.varno_source = 1;
+	context.varno_target = 2;
+	context.varno_join = 3;
+
+	context.offset_source = 0;
+
+	
+	context.offset_target = list_length(source_rte->eref->colnames);
+
+	push_up_merge_action_vars_walker(actplan->plan.targetlist, &context);
+	
+	push_up_merge_action_vars_walker(actplan->plan.qual, &context);
+	
+}
+
+
+static bool
+push_up_merge_action_vars_walker(Node *node, 
+									push_up_merge_action_vars_context *context)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, Var))
+	{
+		Var *var = (Var *)node;
+
+		if(var->varno == context->varno_source)
+		{
+			var->varno = context->varno_join;
+			var->varattno += context->offset_source;
+			return false;
+		}
+		else if(var->varno == context->varno_target)
+		{
+			var->varno = context->varno_join;
+			var->varattno += context->offset_target;
+			return false;
+		}
+		else if(var->varno == context->varno_join)
+			return false;
+		else
+			elog(ERROR, "the vars in merge action tlist of qual should only belongs to the source table or targe table");
+		
+		
+	}
+	
+	return expression_tree_walker(node, push_up_merge_action_vars_walker,
+								  (void *) context);
+}
+
 
 /*
  * flatten_join_alias_vars
diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 6b99a10..58d7a49 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -47,6 +47,7 @@ static Query *transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt);
 static Query *transformInsertStmt(ParseState *pstate, InsertStmt *stmt);
 static List *transformInsertRow(ParseState *pstate, List *exprlist,
 				   List *stmtcols, List *icolumns, List *attrnos);
+static Query *transformMergeStmt(ParseState *pstate, MergeStmt *stmt);
 static Query *transformSelectStmt(ParseState *pstate, SelectStmt *stmt);
 static Query *transformValuesClause(ParseState *pstate, SelectStmt *stmt);
 static Query *transformSetOperationStmt(ParseState *pstate, SelectStmt *stmt);
@@ -164,17 +165,24 @@ transformStmt(ParseState *pstate, Node *parseTree)
 			 * Optimizable statements
 			 */
 		case T_InsertStmt:
+		case T_MergeInsert:
 			result = transformInsertStmt(pstate, (InsertStmt *) parseTree);
 			break;
 
 		case T_DeleteStmt:
+		case T_MergeDelete:
 			result = transformDeleteStmt(pstate, (DeleteStmt *) parseTree);
 			break;
 
 		case T_UpdateStmt:
+		case T_MergeUpdate:
 			result = transformUpdateStmt(pstate, (UpdateStmt *) parseTree);
 			break;
 
+		case T_MergeStmt:
+			result = transformMergeStmt(pstate, (MergeStmt *)parseTree);
+			break; 
+
 		case T_SelectStmt:
 			{
 				SelectStmt *n = (SelectStmt *) parseTree;
@@ -282,22 +290,33 @@ transformDeleteStmt(ParseState *pstate, DeleteStmt *stmt)
 
 	qry->commandType = CMD_DELETE;
 
-	/* set up range table with just the result rel */
-	qry->resultRelation = setTargetTable(pstate, stmt->relation,
-								  interpretInhOption(stmt->relation->inhOpt),
-										 true,
-										 ACL_DELETE);
-
 	qry->distinctClause = NIL;
 
+	if(IsA(stmt,MergeDelete))
+		qry->isMergeAction = true;
 	/*
-	 * The USING clause is non-standard SQL syntax, and is equivalent in
-	 * functionality to the FROM list that can be specified for UPDATE. The
-	 * USING keyword is used rather than FROM because FROM is already a
-	 * keyword in the DELETE syntax.
-	 */
-	transformFromClause(pstate, stmt->usingClause);
+	* The input stmt could be a MergeDelete node. 
+	* In this case, we don't need the process on range table.
+	*/
+	if(IsA(stmt, DeleteStmt))
+	{
+		/* set up range table with just the result rel */
+		qry->resultRelation = setTargetTable(pstate, stmt->relation,
+									  interpretInhOption(stmt->relation->inhOpt),
+											 true,
+											 ACL_DELETE);
 
+		
+
+		/*
+		 * The USING clause is non-standard SQL syntax, and is equivalent in
+		 * functionality to the FROM list that can be specified for UPDATE. The
+		 * USING keyword is used rather than FROM because FROM is already a
+		 * keyword in the DELETE syntax.
+		 */
+		transformFromClause(pstate, stmt->usingClause);
+	}
+	
 	qual = transformWhereClause(pstate, stmt->whereClause, "WHERE");
 
 	qry->returningList = transformReturningList(pstate, stmt->returningList);
@@ -342,11 +361,16 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 	qry->commandType = CMD_INSERT;
 	pstate->p_is_insert = true;
 
+	if(IsA(stmt,MergeInsert))
+		qry->isMergeAction = true;
+	
 	/*
 	 * We have three cases to deal with: DEFAULT VALUES (selectStmt == NULL),
 	 * VALUES list, or general SELECT input.  We special-case VALUES, both for
 	 * efficiency and so we can handle DEFAULT specifications.
 	 */
+
+	/*a MergeInsert statment is always a VALUE clause*/
 	isGeneralSelect = (selectStmt && selectStmt->valuesLists == NIL);
 
 	/*
@@ -382,7 +406,8 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 	 * mentioned in the SELECT part.  Note that the target table is not added
 	 * to the joinlist or namespace.
 	 */
-	qry->resultRelation = setTargetTable(pstate, stmt->relation,
+	if(IsA(stmt,InsertStmt))/*for MergeInsert, no need to do this*/ 
+		qry->resultRelation = setTargetTable(pstate, stmt->relation,
 										 false, false, ACL_INSERT);
 
 	/* Validate stmt->cols list, or build default list if no list given */
@@ -1730,16 +1755,23 @@ transformUpdateStmt(ParseState *pstate, UpdateStmt *stmt)
 	qry->commandType = CMD_UPDATE;
 	pstate->p_is_update = true;
 
-	qry->resultRelation = setTargetTable(pstate, stmt->relation,
-								  interpretInhOption(stmt->relation->inhOpt),
-										 true,
-										 ACL_UPDATE);
+	if(IsA(stmt,MergeUpdate))
+		qry->isMergeAction = true;
 
-	/*
-	 * the FROM clause is non-standard SQL syntax. We used to be able to do
-	 * this with REPLACE in POSTQUEL so we keep the feature.
-	 */
-	transformFromClause(pstate, stmt->fromClause);
+	
+	if(IsA(stmt, UpdateStmt))/*for MergeUpdate, no need to do this*/
+	{
+		qry->resultRelation = setTargetTable(pstate, stmt->relation,
+									  interpretInhOption(stmt->relation->inhOpt),
+											 true,
+											 ACL_UPDATE);
+
+		/*
+		 * the FROM clause is non-standard SQL syntax. We used to be able to do
+		 * this with REPLACE in POSTQUEL so we keep the feature.
+		 */
+		transformFromClause(pstate, stmt->fromClause);
+	}
 
 	qry->targetList = transformTargetList(pstate, stmt->targetList);
 
@@ -2241,3 +2273,304 @@ applyLockingClause(Query *qry, Index rtindex,
 	rc->pushedDown = pushedDown;
 	qry->rowMarks = lappend(qry->rowMarks, rc);
 }
+
+
+
+/*transform a action of merge command into a query. 
+No change of the pstate range table is allowed in this function. 
+*/
+static Query *
+transformMergeActions(ParseState *pstate, MergeStmt *stmt, MergeConditionAction *condact)
+{
+	Query *actqry = makeNode(Query);
+	A_Expr *match_expr; 
+	A_Expr *act_qual_expr;
+
+	/*
+	*	firstly, we need to make sure that DELETE and UPDATE 
+	*	actions are only taken in MATCHED condition, 
+	*	and INSERTs are only takend when not MATCHED
+	*/
+	if(IsA(condact->action, MergeDelete)) 
+	{	
+		if(!condact->match) 
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+		 		errmsg("The DELETE action in MERGE command is not allowed when NOT MATCHED")));
+	}
+	else if(IsA(condact->action, MergeUpdate))
+	{	
+		if(!condact->match) 
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+		 		errmsg("The UPDATE action in MERGE command is not allowed when NOT MATCHED")));
+	}
+	else if(IsA(condact->action, MergeInsert))
+	{	
+		if(condact->match) 
+			ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+		 		errmsg("The INSERT action in MERGE command is not allowed when MATCHED")));
+	}
+	else
+		ereport(ERROR,
+			(errcode(ERRCODE_SYNTAX_ERROR),
+			 errmsg("UNKONWN action type in MERGE")));
+
+
+		
+	act_qual_expr = condact->condition;
+	
+	/*use the transfomStmt() to parse all types of actions*/
+	if(IsA(condact->action, MergeDelete))
+	{
+		/*a delete action*/
+		MergeDelete *deleteact = (MergeDelete *)(condact->action);
+		Assert(IsA(deleteact,DeleteStmt));
+		
+		deleteact->relation = stmt->relation;
+		deleteact->usingClause = stmt->source;
+		deleteact->whereClause = (Node *)act_qual_expr;
+
+		/*parse the action query*/
+		actqry = transformStmt(pstate, (Node *)deleteact);
+
+		if(!IsA(actqry, Query) || actqry->commandType != CMD_DELETE || actqry->utilityStmt != NULL)
+			elog(ERROR, "improper DELETE action in merge stmt");
+
+		return actqry;
+	}
+	else if(IsA(condact->action, MergeUpdate))
+	{
+		/*an update action*/
+		MergeUpdate *updateact = (MergeUpdate *)(condact->action);
+
+		/*the "targetlist" of the updateact is filled in the parser */
+		updateact->relation = stmt->relation;
+		updateact->fromClause = stmt->source;
+		updateact->whereClause = (Node *)act_qual_expr;
+
+		/*parse the action query*/
+		actqry = transformStmt(pstate, (Node *)updateact);
+
+		if(!IsA(actqry, Query) || actqry->commandType != CMD_UPDATE|| actqry->utilityStmt != NULL)
+			elog(ERROR, "improper UPDATE action in merge stmt");
+
+		return actqry;
+	}
+	else if(IsA(condact->action, MergeInsert))
+	{
+		/*an insert action*/
+		Node *qual;
+		MergeInsert *insertact;
+
+		insertact = (MergeInsert *)(condact->action);
+		
+		
+		/*the "cols" and "selectStmt" of the insertact is filled in the parser */
+		insertact->relation = stmt->relation;
+
+		/*
+		the merge insert action has a strange feature. 
+		In an ordinary INSERT, the VALUES list can only contains constants and DEFAULT. (am I right??)
+		But in the INSERT action of MERGE command, the VALUES list can have expressions with variables(attributes of the targe and source tables).
+		Besides, in the ordinary INSERT, a VALUES list can never be followed by a WHERE clause. But in MERGE INSERT action, there are matching conditions. 
+
+		Thus, the output qry of this function is an INSERT query in the style of "INSERT...VALUES...", except that we have other range tables and a WHERE clause.
+		Note that it is also different from the "INSERT ... SELECT..." query, in which the whole SELECT is a subquery. (We don't have subquery here).
+		We construct this novel query structure in order to keep consitency with other merge action types (DELETE, UPDATE). 
+		In this way, all the merge action queries are in fact share the very same Range Table, They only differs in their target lists and join trees
+		
+		*/
+		
+				
+		/*parse the action query, this will call transformInsertStmt() which analyzes the VALUES list.*/
+		actqry = transformStmt(pstate, (Node *)insertact);
+
+		/*do the WHERE clause here, Since the transformInsertStmt() function 
+		only analyzes the VALUES list but not the WHERE clause*/
+		qual = transformWhereClause(pstate,(Node *)act_qual_expr, "WHERE");
+		
+		actqry->jointree = makeFromExpr(pstate->p_joinlist, qual);
+
+		if(!IsA(actqry, Query) || actqry->commandType != CMD_INSERT|| actqry->utilityStmt != NULL)
+			elog(ERROR, "improper INSERT action in merge stmt");
+
+
+		return actqry;
+	}
+	else
+		elog(ERROR, "unknown action type in MERGE");
+
+	/*never comes here*/
+	return NULL;
+}
+
+
+
+static Query *
+transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
+{
+	Query	   *qry; 
+
+	ColumnRef *starRef;
+	ResTarget *starResTarget;
+	ListCell *act;
+	ListCell *l;
+	JoinExpr *joinexp;
+	int 	rtindex;
+
+	/*this will never happen, since the garm.y is restricted that only one rel name is allowed to appear in the source table position. 
+	However, if we extent the command in future, we may need to note this check here. 
+	*/
+	if(list_length(stmt->source) != 1) 
+		ereport(ERROR,
+			(errcode(ERRCODE_SYNTAX_ERROR),
+			 errmsg("now we only accept merge command with only ONE source table")));
+		
+	/*now, do the real tranformation of the merge command. */
+	qry = makeNode(Query);
+	qry->commandType = CMD_MERGE;
+
+	/*
+	What we are doing here is to create a query like 
+		"SELECT * FROM <source_rel> LEFT JOIN <target_rel> ON <match_condition>;"
+	Note:	
+	1. we set the "match condition" as the join qualification. 
+	The left join will scan both the matched and non-matched tuples.
+
+	2. a normal SELECT query has no "target relation". 
+	But here we need to set the targe relation in query, like the UPDATE/DELETE/INSERT queries. 
+	So this is a left join SELECT with a "target table" in its range table. 
+
+	3. We don't have a specific ACL level for Merge, here we just use ACL_SELECT. 
+	But we will add other ACL levels when handle each merge actions.  
+	*/
+
+
+	/*before analyze the FROM clause, we need to set the target table. 
+	We cannot call setTargetTable() function directly. 
+	We only need the lock target relation, without adding it to Range table. 
+	*/
+	
+	
+	setTargetTableLock(pstate, stmt->relation);
+	
+	
+	
+	/*create the FROM clause. Make the join expression first*/
+	joinexp = makeNode(JoinExpr);
+	joinexp->jointype = JOIN_LEFT;
+	joinexp->isNatural = FALSE;
+	joinexp->larg = linitial(stmt->source);/*source list has only one element*/
+	joinexp->rarg = (Node *)stmt->relation;
+	joinexp->quals = stmt->matchCondition; /*match condtion*/
+
+	/*transform the FROM clause. The target relation and source relation will be add to Rtable here.	*/
+	transformFromClause(pstate, list_make1(joinexp));
+
+	/*the targetList of the main query is "*"	  
+	*/
+	starRef = makeNode(ColumnRef);	
+	starRef->fields = list_make1(makeNode(A_Star));					
+	starRef->location = 1;					
+
+	starResTarget = makeNode(ResTarget);					
+	starResTarget->name = NULL;					
+	starResTarget->indirection = NIL;					
+	starResTarget->val = (Node *)starRef;					
+	starResTarget->location = 1;
+	
+	qry->targetList = transformTargetList(pstate, list_make1(starResTarget));
+
+	/*we don't need the WHERE clause here. Set it null. */
+	qry->jointree = makeFromExpr(pstate->p_joinlist, NULL);
+
+	/*now , we find out the RTE for the target relation, and do some unfinished jobs*/
+	rtindex = 1;
+	foreach(l, pstate->p_rtable)
+	{
+		RangeTblEntry *rte = (RangeTblEntry *)lfirst(l);
+		if(rte->relid == pstate->p_target_relation->rd_id) /*find the RTE*/
+		{
+			pstate->p_target_rangetblentry = rte;
+			rte->requiredPerms = ACL_SELECT;	
+			qry->resultRelation = rtindex;
+			break;
+		}
+		rtindex++;
+	}
+
+	if(pstate->p_target_rangetblentry == NULL)
+		elog(ERROR, "cannot find the RTE for target table");
+	
+
+	qry->rtable = pstate->p_rtable;
+
+	qry->hasSubLinks = pstate->p_hasSubLinks;
+
+	/*
+	 * Top-level aggregates are simply disallowed in MERGE
+	 */
+	if (pstate->p_hasAggs)
+		ereport(ERROR,
+				(errcode(ERRCODE_GROUPING_ERROR),
+				 errmsg("cannot use aggregate function in top level of MERGE"),
+				 parser_errposition(pstate,
+									locate_agg_of_level((Node *) qry, 0))));
+	if (pstate->p_hasWindowFuncs)
+		ereport(ERROR,
+				(errcode(ERRCODE_WINDOWING_ERROR),
+				 errmsg("cannot use window function in MERGE"),
+				 parser_errposition(pstate,
+									locate_windowfunc((Node *) qry))));
+
+
+	/*
+		the main query is done.
+	then for each actions ,we transform it to a seperate query.
+	the action queries shares the exactly same range table with the main query. 
+	in other words, in the extra condtions of the sub actions, we don't allow involvement of new tables
+	*/
+	
+	qry->mergeActQry = NIL;
+
+	foreach(act,stmt->actions)
+	{
+		MergeConditionAction *mca = lfirst(act);
+		Query *actqry;
+
+		switch(mca->action->type)
+		{
+			case T_MergeDelete:
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_DELETE;
+				break;
+			case T_MergeUpdate:
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_UPDATE;
+				break;
+			case T_MergeInsert:
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_INSERT;				
+				break;
+			default:
+				elog(ERROR, "unknown MERGE action type %d", mca->type);
+				break;
+
+		}
+
+
+		/*transform the act (and its condition) as a single query. Link it to the top-level query*/
+		actqry = transformMergeActions(pstate, stmt, mca);
+
+		/*since we don't invoke setTargetTable() in transformMergeActions(), we need to set actqry->resultRelation here
+		*/
+		actqry->resultRelation = qry->resultRelation;
+
+		qry->mergeActQry = lappend(qry->mergeActQry, actqry);
+	}
+	
+	return qry;
+
+	
+}
+
+
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 1722036..166ca3e 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -212,6 +212,10 @@ static TypeName *TableFuncTypeName(List *columns);
 		DropOwnedStmt ReassignOwnedStmt
 		AlterTSConfigurationStmt AlterTSDictionaryStmt
 
+%type <node>	MergeStmt  opt_and_condition  merge_condition_action   merge_action
+%type <boolean> opt_not	
+%type <list> 	merge_condition_action_list
+
 %type <node>	select_no_parens select_with_parens select_clause
 				simple_select values_clause
 
@@ -504,6 +508,8 @@ static TypeName *TableFuncTypeName(List *columns);
 
 	MAPPING MATCH MAXVALUE MINUTE_P MINVALUE MODE MONTH_P MOVE
 
+	MATCHED MERGE
+	
 	NAME_P NAMES NATIONAL NATURAL NCHAR NEXT NO NOCREATEDB
 	NOCREATEROLE NOCREATEUSER NOINHERIT NOLOGIN_P NONE NOSUPERUSER
 	NOT NOTHING NOTIFY NOTNULL NOWAIT NULL_P NULLIF NULLS_P NUMERIC
@@ -725,6 +731,7 @@ stmt :
 			| ListenStmt
 			| LoadStmt
 			| LockStmt
+			| MergeStmt 
 			| NotifyStmt
 			| PrepareStmt
 			| ReassignOwnedStmt
@@ -6985,6 +6992,7 @@ ExplainableStmt:
 			| InsertStmt
 			| UpdateStmt
 			| DeleteStmt
+			| MergeStmt
 			| DeclareCursorStmt
 			| CreateAsStmt
 			| ExecuteStmt					/* by default all are $$=$1 */
@@ -7330,6 +7338,101 @@ set_target_list:
 /*****************************************************************************
  *
  *		QUERY:
+ *				MERGE STATEMENT
+ *
+ *****************************************************************************/
+
+
+MergeStmt: 
+			MERGE INTO relation_expr_opt_alias
+			USING  table_ref
+			ON a_expr
+			merge_condition_action_list
+				{
+					MergeStmt *m = makeNode(MergeStmt);
+
+					m->relation = $3;
+					m->source = list_make1($5);  /*although we have only one USING table, but we still make it a list, maybe in future we will allow mutliple USING tables.*/
+					m->matchCondition = $7;
+					m->actions = $8;
+
+					$$ = (Node *)m;
+				}
+				;
+	
+merge_condition_action_list: 
+							merge_condition_action 		
+								{ $$ = list_make1($1); }
+							| merge_condition_action_list merge_condition_action   
+								{ $$ = lappend($1,$2); }
+							;	
+
+merge_condition_action: 	
+							WHEN opt_not MATCHED opt_and_condition THEN merge_action
+							{
+								MergeConditionAction *m = makeNode(MergeConditionAction);
+
+								m->match = $2;
+								m->condition = $4;
+								m->action = $6;
+
+								$$ = (Node *)m;
+							}
+							;
+
+
+opt_and_condition:	
+					AND a_expr 		{$$ = $2;}
+					| /*EMPTY*/ 		{$$ = NULL;}
+					;
+
+opt_not:	
+			NOT			{$$ = false;}
+			| /*EMPTY*/	{$$ = true;}
+			;
+
+merge_action: 	
+				DELETE_P	
+					{$$ = (Node *)makeNode(MergeDelete);}
+				| UPDATE SET set_clause_list 
+					{
+						UpdateStmt *n = makeNode(MergeUpdate);
+						n->targetList = $3;
+						$$ = (Node *)n;
+					}
+				| INSERT values_clause
+					{
+						InsertStmt *n = makeNode(MergeInsert);
+						n->cols = NIL;
+						n->selectStmt = $2;
+
+						$$ = (Node *)n;
+					}
+					
+				| INSERT '(' insert_column_list ')' values_clause
+					{
+						InsertStmt *n = makeNode(MergeInsert);
+						n->cols = $3;
+						n->selectStmt = $5;
+
+						$$ = (Node *)n;
+					}
+				| INSERT DEFAULT VALUES
+					{
+						InsertStmt *n = makeNode(MergeInsert);
+						n->cols = NIL;
+						n->selectStmt = NULL;
+
+						$$ = (Node *)n; 
+					}
+					
+				;	
+				
+
+
+/*****************************************************************************
+ *
+ *		QUERY:
  *				CURSOR STATEMENTS
  *
  *****************************************************************************/
@@ -10968,7 +11071,9 @@ unreserved_keyword:
 			| LOGIN_P
 			| MAPPING
 			| MATCH
+			| MATCHED
 			| MAXVALUE
+			| MERGE
 			| MINUTE_P
 			| MINVALUE
 			| MODE
diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index 16ca583..92b4e20 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -214,6 +214,29 @@ setTargetTable(ParseState *pstate, RangeVar *relation,
 	return rtindex;
 }
 
+
+void
+setTargetTableLock(ParseState *pstate, RangeVar *relation)
+{
+	
+	/* Close old target; this could only happen for multi-action rules */
+	if (pstate->p_target_relation != NULL)
+		heap_close(pstate->p_target_relation, NoLock);
+
+	/*
+	 * Open target rel and grab suitable lock (which we will hold till end of
+	 * transaction).
+	 *
+	 * free_parsestate() will eventually do the corresponding heap_close(),
+	 * but *not* release the lock.
+	 */
+	pstate->p_target_relation = parserOpenTable(pstate, relation,
+												RowExclusiveLock);
+
+	
+}
+
+
 /*
  * Simplify InhOption (yes/no/default) into boolean yes/no.
  *
diff --git a/src/backend/rewrite/rewriteHandler.c b/src/backend/rewrite/rewriteHandler.c
index 25b44dd..9e3b30b 100644
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -1837,6 +1837,45 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 }
 
 
+#define insert_rewrite (1<<0) /*insert merge action has already been processed by rewriter*/
+#define delete_rewrite (1<<1) 
+#define update_rewrite (1<<2)
+
+#define	insert_instead (1<<3) /*insert merge action is fully replace by rules.*/
+#define delete_instead (1<<4)
+#define update_instead (1<<5)
+
+
+#define merge_action_already_rewrite(acttype, flag) \
+	((acttype == CMD_INSERT && (flag & insert_rewrite)) || \
+		(acttype == CMD_UPDATE && (flag & update_rewrite)) || \
+		(acttype == CMD_DELETE && (flag & delete_rewrite)))
+
+
+#define set_action_rewrite(acttype, flag)	\
+				if(acttype == CMD_INSERT)  \
+					{flag |= insert_rewrite;}\
+				else if(acttype == CMD_UPDATE)  \
+					{flag |= update_rewrite;}\
+				else if(acttype == CMD_DELETE)  \
+					{flag |= delete_rewrite;}
+
+
+				
+#define merge_action_instead(acttype, flag)		\
+			((acttype == CMD_INSERT && (flag & insert_instead)) || \
+				(acttype == CMD_UPDATE && (flag & update_instead)) || \
+				(acttype == CMD_DELETE && (flag & delete_instead)))
+
+#define set_action_instead(acttype, flag)\
+				if(acttype == CMD_INSERT)  \
+					{flag |= insert_instead;}\
+				else if(acttype == CMD_UPDATE)  \
+					{flag |= update_instead;}\
+				else if(acttype == CMD_DELETE)  \
+					{flag |= delete_instead;}
+
+
 /*
  * QueryRewrite -
  *	  Primary entry point to the query rewriter.
@@ -1861,7 +1900,149 @@ QueryRewrite(Query *parsetree)
 	 *
 	 * Apply all non-SELECT rules possibly getting 0 or many queries
 	 */
-	querylist = RewriteQuery(parsetree, NIL);
+
+	
+	if(parsetree->commandType == CMD_MERGE)
+	{
+		/*
+		*for merge query, we have a set of action queries (not subquery).
+		*each of these action queries should be applied to RewriteQuery(). 
+		*/
+		ListCell   *cell,
+				   *prev,
+				   *next;
+
+		int flag = 0;
+
+		
+		List *pre_qry = NIL;
+		List *post_qry = NIL;
+
+
+		querylist = NIL;
+		
+
+		/*rewrite the merge action queries one by one.*/
+		prev = NULL;
+
+		for (cell = list_head(parsetree->mergeActQry); cell; cell = next)
+		{
+			List *queryList4action = NIL;
+			Query *actionqry;
+			Query *q;
+
+			
+			actionqry = lfirst(cell);
+
+			next = lnext(cell);
+
+			/*if this kind of actions are fully replaced by rules, we delete it from the action list*/	
+			if(merge_action_instead(actionqry->commandType, flag))
+			{
+				parsetree->mergeActQry = list_delete_cell(parsetree->mergeActQry, cell, prev);
+				continue;
+			}
+
+
+			/*if this kind of actions are already processed by rewriter, skip it.*/
+			if(merge_action_already_rewrite(actionqry->commandType, flag))
+			{
+				/*	Still need to call RewriteQuery(), since we need the process on target list and so on. 
+					BUT, the returned list is discarded
+				*/
+				RewriteQuery(actionqry, NIL);
+			
+				prev = cell; 
+				continue;
+			}
+
+			/*ok this action has not been processed before, let's do it now.*/
+			queryList4action = RewriteQuery(actionqry, NIL);
+
+			/*this kind of actions has been processed.*/
+			set_action_rewrite(actionqry->commandType,flag); 
+
+			/*if the returning list is nil, this merge action is replaced by a do-nothing rule*/
+			if(queryList4action == NIL) 
+			{
+				/*set the flag for other merge actions of the same type*/
+				set_action_instead(actionqry->commandType, flag);
+
+				/*delete the action.*/
+				parsetree->mergeActQry = list_delete_cell(parsetree->mergeActQry, cell, prev);
+
+				continue;
+			}
+
+			
+			/*the merge action query could be one of the elements in the rewriten list. 
+			*if it is in the list, it must be the head or tail.
+			*/
+			q = (Query *)linitial(queryList4action);
+			if(q->querySource == QSRC_ORIGINAL)
+			{
+				/*
+				*the merge action is the head, the remaining part of the list are the queries generated by rules
+				*we put them in the post_qry list. 
+				*/
+				if(querylist == NIL)
+					querylist = list_make1(parsetree);
+
+
+				queryList4action = list_delete_first(queryList4action);
+				post_qry = list_concat(post_qry,queryList4action);
+				prev = cell; 
+				continue;
+
+			}
+			
+			
+			q = (Query *)llast(queryList4action);
+			if(q->querySource == QSRC_ORIGINAL)
+			{
+				/*the merge action is the tail. Put the rule queries in pre_qry list*/
+
+				if(querylist == NIL)
+					querylist = list_make1(parsetree);
+					
+				queryList4action = list_truncate(queryList4action,list_length(queryList4action)-1);
+
+				pre_qry = list_concat(pre_qry,queryList4action);
+
+				prev = cell; 
+				continue;
+
+			}	
+				
+
+			/*here, the merge action query is not in the rewriten query list, 
+			*which means the action should be deleted.
+			*It is replaced by INSTEAD rule(s). We need to delete the action  
+
+				For a INSERT action, we put the rule queries in the post list
+				otherwise, in the pre list
+			*/
+			if(actionqry->commandType == CMD_INSERT)
+				post_qry = list_concat(post_qry,queryList4action);
+			else
+				pre_qry = list_concat(pre_qry,queryList4action);
+			
+			set_action_instead(actionqry->commandType, flag);
+			parsetree->mergeActQry = list_delete_cell(parsetree->mergeActQry, cell, prev);
+		}				
+
+		
+
+		/*finally, put the 3 lists into one. 
+		*If all the merge actions are replaced by rules, the original merge query 
+		*will not be involved in the querylist.
+		*/
+		querylist = list_concat(pre_qry,querylist);
+		querylist = list_concat(querylist, post_qry);
+			
+	}
+	else
+		querylist = RewriteQuery(parsetree, NIL);
 
 	/*
 	 * Step 2
diff --git a/src/backend/tcop/pquery.c b/src/backend/tcop/pquery.c
index 8ad4915..0dc3117 100644
--- a/src/backend/tcop/pquery.c
+++ b/src/backend/tcop/pquery.c
@@ -225,6 +225,10 @@ ProcessQuery(PlannedStmt *plan,
 				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
 						 "DELETE %u", queryDesc->estate->es_processed);
 				break;
+			case CMD_MERGE:
+				snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
+						 "MERGE %u", queryDesc->estate->es_processed);
+				break;
 			default:
 				strcpy(completionTag, "???");
 				break;
diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c
index 1815539..e0dc7c3 100644
--- a/src/backend/tcop/utility.c
+++ b/src/backend/tcop/utility.c
@@ -125,6 +125,7 @@ CommandIsReadOnly(Node *parsetree)
 			case CMD_UPDATE:
 			case CMD_INSERT:
 			case CMD_DELETE:
+			case CMD_MERGE:
 				return false;
 			default:
 				elog(WARNING, "unrecognized commandType: %d",
@@ -1405,6 +1406,10 @@ CreateCommandTag(Node *parsetree)
 			tag = "SELECT";
 			break;
 
+		case T_MergeStmt:
+			tag = "MERGE";
+			break;
+		
 			/* utility statements --- same whether raw or cooked */
 		case T_TransactionStmt:
 			{
@@ -2242,6 +2247,7 @@ GetCommandLogLevel(Node *parsetree)
 		case T_InsertStmt:
 		case T_DeleteStmt:
 		case T_UpdateStmt:
+		case T_MergeStmt:
 			lev = LOGSTMT_MOD;
 			break;
 
diff --git a/src/include/executor/nodeModifyTable.h b/src/include/executor/nodeModifyTable.h
index 67ba3e8..92f50ed 100644
--- a/src/include/executor/nodeModifyTable.h
+++ b/src/include/executor/nodeModifyTable.h
@@ -16,6 +16,9 @@
 #include "nodes/execnodes.h"
 
 extern ModifyTableState *ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags);
+
+extern MergeActionState *ExecInitMergeAction(MergeAction *node, EState *estate, int eflags);
+
 extern TupleTableSlot *ExecModifyTable(ModifyTableState *node);
 extern void ExecEndModifyTable(ModifyTableState *node);
 extern void ExecReScanModifyTable(ModifyTableState *node);
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 7442d2d..7f661f3 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1032,9 +1032,22 @@ typedef struct ModifyTableState
 	int			mt_whichplan;	/* which one is being executed (0..n-1) */
 	EPQState	mt_epqstate;	/* for evaluating EvalPlanQual rechecks */
 	bool		fireBSTriggers; /* do we need to fire stmt triggers? */
+	List 		*mergeActPstates; /*the list of the planstate of meger command actions. 
+									NIL if this is not a merge command.
+									The elements if it are MergeActionState nodes*/
 } ModifyTableState;
 
 /* ----------------
+ *	 MergeActionState information
+ * ----------------
+ */
+typedef struct MergeActionState
+{
+	PlanState	ps;				/* its first field is NodeTag */
+	CmdType		operation;	
+} MergeActionState;
+
+/* ----------------
  *	 AppendState information
  *
  *		nplans			how many plans are in the array
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index a5f5df5..053eee7 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -44,6 +44,7 @@ typedef enum NodeTag
 	T_Plan = 100,
 	T_Result,
 	T_ModifyTable,
+	T_MergeAction,
 	T_Append,
 	T_RecursiveUnion,
 	T_BitmapAnd,
@@ -86,6 +87,7 @@ typedef enum NodeTag
 	T_PlanState = 200,
 	T_ResultState,
 	T_ModifyTableState,
+	T_MergeActionState,
 	T_AppendState,
 	T_RecursiveUnionState,
 	T_BitmapAndState,
@@ -347,6 +349,14 @@ typedef enum NodeTag
 	T_AlterUserMappingStmt,
 	T_DropUserMappingStmt,
 	T_AlterTableSpaceOptionsStmt,
+		
+	T_MergeStmt,
+	T_MergeConditionAction,
+	T_MergeUpdate, 
+	T_MergeDelete,	
+	T_MergeInsert,
+		
+		
 
 	/*
 	 * TAGS FOR PARSE TREE NODES (parsenodes.h)
@@ -511,6 +521,7 @@ typedef enum CmdType
 	CMD_UPDATE,					/* update stmt */
 	CMD_INSERT,					/* insert stmt */
 	CMD_DELETE,
+	CMD_MERGE,						/*merge stmt*/
 	CMD_UTILITY,				/* cmds like create, destroy, copy, vacuum,
 								 * etc. */
 	CMD_NOTHING					/* dummy command for instead nothing rules
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index fec8d3c..287033f 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -146,6 +146,11 @@ typedef struct Query
 
 	Node	   *setOperations;	/* set-operation tree if this is top level of
 								 * a UNION/INTERSECT/EXCEPT query */
+
+	bool		 isMergeAction; /*if this query is a merge action. */	 
+
+	List 		*mergeActQry; /* the list of all the merge actions. 
+								* used only for merge query statment*/							 
 } Query;
 
 
@@ -990,6 +995,44 @@ typedef struct SelectStmt
 	/* Eventually add fields for CORRESPONDING spec here */
 } SelectStmt;
 
+/*The structure for MERGE command statement*/
+typedef struct MergeStmt
+{
+	NodeTag		type;
+	RangeVar   	*relation;		/*targe relation for merge */
+
+	/* source relations for the merge. 
+	*Currently, we only allwo single-source merge, 
+	*so the length of this list should always be 1 
+	*/
+	List		*source;		
+	Node	   	*matchCondition;	/* qualifications of the merge*/
+
+	/*list  of MergeConditionAction structure. 
+	*It stores all the matched / not-matched conditions and the corresponding actions
+	*The elments of this list are MergeConditionAction nodes
+	*/
+	List	   	*actions;		
+
+}MergeStmt;
+
+/*	the structure for the actions of MERGE command. 
+*	Holds info of the clauses like "... WHEN MATCHED AND ... THEN UPDATE/DELETE/INSERT"
+*/
+typedef struct MergeConditionAction
+{
+	NodeTag		type;
+	bool 		match; /*match or not match*/
+	Node		*condition;/*the AND condition for this action*/
+	Node 		*action; /*the actions: delete , insert or update*/
+}MergeConditionAction;
+
+/*
+*	The merge action nodes are in fact the ordinary nodes of UPDATE,DELETE and INSERT
+*/
+typedef UpdateStmt MergeUpdate;
+typedef DeleteStmt MergeDelete;
+typedef InsertStmt MergeInsert;
 
 /* ----------------------
  *		Set Operation node for post-analysis query trees
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 037bc0b..5a73d60 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -169,9 +169,22 @@ typedef struct ModifyTable
 	List	   *returningLists; /* per-target-table RETURNING tlists */
 	List	   *rowMarks;		/* PlanRowMarks (non-locking only) */
 	int			epqParam;		/* ID of Param for EvalPlanQual re-eval */
+	List 		*mergeActPlan;	/*the plans for merge actions, which are also ModifyTable nodes*/
 } ModifyTable;
 
 /* ----------------
+ *	 MergeAction node -
+ *		The plan node for the actions of MERGE command
+ * ----------------
+ */
+typedef struct MergeAction
+{
+	Plan plan;
+	CmdType	operation;/* INSERT, UPDATE, or DELETE */
+	List *flattenedqual; /*the flattened qual expression of action*/
+}MergeAction;
+
+/* ----------------
  *	 Append node -
  *		Generate the concatenation of the results of sub-plans.
  * ----------------
diff --git a/src/include/optimizer/planner.h b/src/include/optimizer/planner.h
index 805dee7..6d7ff4f 100644
--- a/src/include/optimizer/planner.h
+++ b/src/include/optimizer/planner.h
@@ -34,6 +34,7 @@ extern Plan *subquery_planner(PlannerGlobal *glob, Query *parse,
 				 PlannerInfo *parent_root,
 				 bool hasRecursion, double tuple_fraction,
 				 PlannerInfo **subroot);
+extern ModifyTable *merge_action_planner(PlannerGlobal *glob, Query *parse, Plan *top_plan);
 
 extern Expr *expression_planner(Expr *expr);
 
diff --git a/src/include/optimizer/var.h b/src/include/optimizer/var.h
index b0e04a0..4d6c9e8 100644
--- a/src/include/optimizer/var.h
+++ b/src/include/optimizer/var.h
@@ -15,6 +15,7 @@
 #define VAR_H
 
 #include "nodes/relation.h"
+#include "nodes/plannodes.h"
 
 typedef enum
 {
@@ -32,5 +33,5 @@ extern int	locate_var_of_relation(Node *node, int relid, int levelsup);
 extern int	find_minimum_var_level(Node *node);
 extern List *pull_var_clause(Node *node, PVCPlaceHolderBehavior behavior);
 extern Node *flatten_join_alias_vars(PlannerInfo *root, Node *node);
-
+extern void push_up_merge_action_vars(MergeAction * actplan,Query * actqry);
 #endif   /* VAR_H */
diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 49d4b6c..436d459 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -229,7 +229,9 @@ PG_KEYWORD("lock", LOCK_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("login", LOGIN_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("mapping", MAPPING, UNRESERVED_KEYWORD)
 PG_KEYWORD("match", MATCH, UNRESERVED_KEYWORD)
+PG_KEYWORD("matched", MATCHED, UNRESERVED_KEYWORD)
 PG_KEYWORD("maxvalue", MAXVALUE, UNRESERVED_KEYWORD)
+PG_KEYWORD("merge", MERGE, UNRESERVED_KEYWORD)
 PG_KEYWORD("minute", MINUTE_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("minvalue", MINVALUE, UNRESERVED_KEYWORD)
 PG_KEYWORD("mode", MODE, UNRESERVED_KEYWORD)
diff --git a/src/include/parser/parse_clause.h b/src/include/parser/parse_clause.h
index f3d3ee9..e4312d8 100644
--- a/src/include/parser/parse_clause.h
+++ b/src/include/parser/parse_clause.h
@@ -19,6 +19,8 @@
 extern void transformFromClause(ParseState *pstate, List *frmList);
 extern int setTargetTable(ParseState *pstate, RangeVar *relation,
 			   bool inh, bool alsoSource, AclMode requiredPerms);
+extern void setTargetTableLock(ParseState *pstate, RangeVar *relation);
+
 extern bool interpretInhOption(InhOption inhOpt);
 extern bool interpretOidsOption(List *defList);
 
diff --git a/src/test/regress/parallel_schedule b/src/test/regress/parallel_schedule
index 7529777..61c7da6 100644
--- a/src/test/regress/parallel_schedule
+++ b/src/test/regress/parallel_schedule
@@ -91,7 +91,7 @@ test: select_views portals_p2 foreign_key cluster dependency guc bitmapops combo
 # NB: temp.sql does a reconnect which transiently uses 2 connections,
 # so keep this parallel group to at most 19 tests
 # ----------
-test: plancache limit plpgsql copy2 temp domain rangefuncs prepare without_oid conversion truncate alter_table sequence polymorphism rowtypes returning largeobject with xml
+test: plancache limit plpgsql copy2 temp domain rangefuncs prepare without_oid conversion truncate alter_table sequence polymorphism rowtypes returning largeobject with xml merge
 
 # run stats by itself because its delay may be insufficient under heavy load
 test: stats
diff --git a/src/test/regress/serial_schedule b/src/test/regress/serial_schedule
index 5f185f9..0fe7006 100644
--- a/src/test/regress/serial_schedule
+++ b/src/test/regress/serial_schedule
@@ -122,4 +122,5 @@ test: returning
 test: largeobject
 test: with
 test: xml
+test: merge
 test: stats
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 0000000..6a85e3e
--- /dev/null
+++ b/src/test/regress/sql/merge.sql
@@ -0,0 +1,51 @@
+--
+-- testing the MERGE INTO ... command
+--
+
+-- Create the test dataset
+
+CREATE TABLE Stock (
+    item_id   INT UNIQUE,
+    balance   INT
+);
+
+INSERT INTO Stock VALUES (10, 1000);
+
+CREATE TABLE Buy (
+    item_id 	INT,
+    amount	  INT
+);
+
+INSERT INTO Buy VALUES (10, 500);
+INSERT INTO Buy VALUES (20, 2000);
+
+CREATE TABLE Sale (
+    item_id 	INT,
+    amount	  INT
+);
+
+INSERT INTO Sale VALUES (10, 1500);
+INSERT INTO Sale VALUES (20, 700);
+
+
+--Test the UPDATE + INSERT operation on stock with MERGE 
+MERGE INTO Stock USING Buy 
+			ON Stock.item_id = Buy.item_id
+ 	WHEN MATCHED THEN UPDATE SET balance = balance + Buy.amount
+ 	WHEN NOT MATCHED THEN INSERT VALUES (Buy.item_id, Buy.amount);
+
+--Look the result
+SELECT * FROM Stock ORDER BY item_id;
+
+
+-- Test the UPDATE+DELETE operation on stock with action quals
+MERGE INTO Stock USING Sale 
+			ON Stock.item_id = Sale.item_id
+   WHEN MATCHED AND balance - amount > 0 THEN UPDATE SET balance = balance - amount
+   WHEN MATCHED THEN DELETE;
+   
+   
+SELECT * FROM STOCK ORDER BY item_id;
+ 
+--clean up
+DROP TABLE Stock, Buy, Sale;

diff --git a/src/test/regress/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index 0000000..18e3891
--- /dev/null
+++ b/src/test/regress/expected/merge.out
@@ -0,0 +1,279 @@
+--
+-- MERGE
+--
+CREATE TABLE target (id integer, balance integer);
+CREATE TABLE source (id integer, balance integer);
+INSERT INTO target VALUES (1, 10);
+INSERT INTO target VALUES (2, 20);
+INSERT INTO target VALUES (3, 30);
+SELECT * FROM target;
+ id | balance 
+----+---------
+  1 |      10
+  2 |      20
+  3 |      30
+(3 rows)
+
+--
+-- initial tests
+--
+-- empty source means 0 rows touched
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance + s.balance
+;
+-- insert some source rows to work from
+INSERT INTO source VALUES (2, 5);
+INSERT INTO source VALUES (3, 20);
+INSERT INTO source VALUES (4, 40);
+SELECT * FROM source;
+ id | balance 
+----+---------
+  2 |       5
+  3 |      20
+  4 |      40
+(3 rows)
+
+-- do a simple equivalent of an UPDATE join
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance + s.balance
+;
+SELECT * FROM target;
+ id | balance 
+----+---------
+  1 |      10
+  2 |      25
+  3 |      50
+(3 rows)
+
+ROLLBACK;
+-- do a simple equivalent of an INSERT SELECT
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+SELECT * FROM target;
+ id | balance 
+----+---------
+  1 |      10
+  2 |      20
+  3 |      30
+  4 |      40
+(4 rows)
+
+ROLLBACK;
+-- now the classic UPSERT
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance + s.balance
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+SELECT * FROM target;
+ id | balance 
+----+---------
+  1 |      10
+  2 |      25
+  3 |      50
+  4 |      40
+(4 rows)
+
+ROLLBACK;
+--
+-- Non-standard functionality
+-- 
+-- do a simple equivalent of a DELETE join
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED THEN
+	DELETE
+;
+SELECT * FROM target;
+ id | balance 
+----+---------
+  1 |      10
+(1 row)
+
+ROLLBACK;
+-- now the classic UPSERT, with a DELETE
+-- the Standard doesn't allow the DELETE clause for some reason,
+-- though other implementations do
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED AND s.balance > 10 THEN
+	UPDATE SET balance = t.balance + s.balance
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+SELECT * FROM target;
+ id | balance 
+----+---------
+  1 |      10
+  3 |      50
+  4 |      40
+(3 rows)
+
+ROLLBACK;
+-- Prepare the test data to generate multiple matching rows for a single target
+INSERT INTO source VALUES (3, 5);
+SELECT * FROM source ORDER BY id, balance;
+ id | balance 
+----+---------
+  2 |       5
+  3 |       5
+  3 |      20
+  4 |      40
+(4 rows)
+
+-- we now have a duplicate key in source, so when we join to
+-- target we will generate 2 matching rows, not one
+-- In the following statement row id=3 will be both updated
+-- and deleted by this statement and so will cause a run-time error
+-- when the second change to that row is detected
+-- This next SQL statement
+--  fails according to standard
+--  fails in PostgreSQL implementation
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED AND s.balance > 10 THEN
+	UPDATE SET balance = t.balance + s.balance
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+ERROR:  multiple actions on single target row
+ 
+ROLLBACK;
+
+-- This next SQL statement
+--  fails according to standard
+--  suceeds in PostgreSQL implementation by simply ignoring the second
+--  matching row since it activates no WHEN clause
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED AND s.balance > 10 THEN
+	UPDATE SET balance = t.balance + s.balance
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+ROLLBACK;
+-- Now lets prepare the test data to generate 2 non-matching rows
+DELETE FROM source WHERE id = 3 AND balance = 5;
+INSERT INTO source VALUES (4, 5);
+SELECT * FROM source;
+ id | balance 
+----+---------
+  2 |       5
+  3 |      20
+  4 |       5
+  4 |      40
+(4 rows)
+
+-- This next SQL statement
+--  suceeds according to standard (yes, it is inconsistent)
+--  suceeds in PostgreSQL implementation, though could easily fail if
+--  there was an appropriate unique constraint
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+SELECT * FROM target;
+ id | balance 
+----+---------
+  1 |      10
+  2 |      20
+  3 |      30
+  4 |       5
+  4 |      40
+(5 rows)
+
+ROLLBACK;
+-- This next SQL statement works, but since there is no WHEN clause that
+-- applies to non-matching rows, SQL standard requires us to generate
+-- rows with DEFAULT VALUES for all columns, which is why we support the
+-- syntax DO NOTHING (similar to the way Rules work) in addition
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN NOT MATCHED AND s.balance > 100 THEN
+	INSERT VALUES (s.id, s.balance)
+;
+SELECT * FROM target;
+ id | balance 
+----+---------
+  1 |      10
+  2 |      20
+  3 |      30
+    |
+    |
+(5 rows)
+
+ROLLBACK;
+-- This next SQL statement suceeds, but does nothing since there are
+-- only non-matching rows that do not activate a WHEN clause, so we
+-- provide syntax to just ignore them, rather than allowing data quality
+-- problems
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN NOT MATCHED AND s.balance > 100 THEN
+	INSERT VALUES (s.id, s.balance)
+WHEN NOT MATCHED
+	DO NOTHING
+;
+SELECT * FROM target;
+ id | balance 
+----+---------
+  1 |      10
+  2 |      20
+  3 |      30
+(3 rows)
+
+ROLLBACK;
+--
+-- Weirdness
+--
+-- MERGE statement containing WHEN clauses that are never executable
+-- NOT an error under the standard
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED AND s.balance > 0 THEN
+	UPDATE SET balance = t.balance + s.balance
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+WHEN NOT MATCHED THEN /* never executed because of order of WHEN clauses */
+	INSERT VALUES (s.id, s.balance + 10)
+WHEN MATCHED THEN /* never executed because of order of WHEN clauses */
+	UPDATE SET balance = t.balance + s.balance
+;
diff --git a/src/test/regress/parallel_schedule b/src/test/regress/parallel_schedule
index 7529777..61c7da6 100644
--- a/src/test/regress/parallel_schedule
+++ b/src/test/regress/parallel_schedule
@@ -91,7 +91,7 @@ test: select_views portals_p2 foreign_key cluster dependency guc bitmapops combo
 # NB: temp.sql does a reconnect which transiently uses 2 connections,
 # so keep this parallel group to at most 19 tests
 # ----------
-test: plancache limit plpgsql copy2 temp domain rangefuncs prepare without_oid conversion truncate alter_table sequence polymorphism rowtypes returning largeobject with xml
+test: plancache limit plpgsql copy2 temp domain rangefuncs prepare without_oid conversion truncate alter_table sequence polymorphism rowtypes returning largeobject with xml merge
 
 # run stats by itself because its delay may be insufficient under heavy load
 test: stats
diff --git a/src/test/regress/serial_schedule b/src/test/regress/serial_schedule
index 5f185f9..0fe7006 100644
--- a/src/test/regress/serial_schedule
+++ b/src/test/regress/serial_schedule
@@ -122,4 +122,5 @@ test: returning
 test: largeobject
 test: with
 test: xml
+test: merge
 test: stats
diff --git a/src/test/regress/sql/merge.sql b/src/test/regress/sql/merge.sql
new file mode 100644
index 0000000..7ecd02e
--- /dev/null
+++ b/src/test/regress/sql/merge.sql
@@ -0,0 +1,200 @@
+--
+-- MERGE
+--
+CREATE TABLE target (id integer, balance integer);
+CREATE TABLE source (id integer, balance integer);
+INSERT INTO target VALUES (1, 10);
+INSERT INTO target VALUES (2, 20);
+INSERT INTO target VALUES (3, 30);
+SELECT * FROM target;
+
+--
+-- initial tests
+--
+-- empty source means 0 rows touched
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance + s.balance
+;
+-- insert some source rows to work from
+INSERT INTO source VALUES (2, 5);
+INSERT INTO source VALUES (3, 20);
+INSERT INTO source VALUES (4, 40);
+SELECT * FROM source;
+
+-- do a simple equivalent of an UPDATE join
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance + s.balance
+;
+
+ROLLBACK;
+-- do a simple equivalent of an INSERT SELECT
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+SELECT * FROM target;
+
+ROLLBACK;
+-- now the classic UPSERT
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED THEN
+	UPDATE SET balance = t.balance + s.balance
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+SELECT * FROM target;
+
+ROLLBACK;
+--
+-- Non-standard functionality
+-- 
+-- do a simple equivalent of a DELETE join
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED THEN
+	DELETE
+;
+SELECT * FROM target;
+
+ROLLBACK;
+-- now the classic UPSERT, with a DELETE
+-- the Standard doesn't allow the DELETE clause for some reason,
+-- though other implementations do
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED AND s.balance > 10 THEN
+	UPDATE SET balance = t.balance + s.balance
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+SELECT * FROM target;
+
+ROLLBACK;
+-- Prepare the test data to generate multiple matching rows for a single target
+INSERT INTO source VALUES (3, 5);
+SELECT * FROM source ORDER BY id, balance;
+
+-- we now have a duplicate key in source, so when we join to
+-- target we will generate 2 matching rows, not one
+-- In the following statement row id=3 will be both updated
+-- and deleted by this statement and so will cause a run-time error
+-- when the second change to that row is detected
+-- This next SQL statement
+--  fails according to standard
+--  fails in PostgreSQL implementation
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED AND s.balance > 10 THEN
+	UPDATE SET balance = t.balance + s.balance
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+ERROR:  multiple actions on single target row
+ 
+ROLLBACK;
+
+-- This next SQL statement
+--  fails according to standard
+--  suceeds in PostgreSQL implementation by simply ignoring the second
+--  matching row since it activates no WHEN clause
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED AND s.balance > 10 THEN
+	UPDATE SET balance = t.balance + s.balance
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+ROLLBACK;
+-- Now lets prepare the test data to generate 2 non-matching rows
+DELETE FROM source WHERE id = 3 AND balance = 5;
+INSERT INTO source VALUES (4, 5);
+SELECT * FROM source;
+
+-- This next SQL statement
+--  suceeds according to standard (yes, it is inconsistent)
+--  suceeds in PostgreSQL implementation, though could easily fail if
+--  there was an appropriate unique constraint
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+;
+SELECT * FROM target;
+
+ROLLBACK;
+-- This next SQL statement works, but since there is no WHEN clause that
+-- applies to non-matching rows, SQL standard requires us to generate
+-- rows with DEFAULT VALUES for all columns, which is why we support the
+-- syntax DO NOTHING (similar to the way Rules work) in addition
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN NOT MATCHED AND s.balance > 100 THEN
+	INSERT VALUES (s.id, s.balance)
+;
+SELECT * FROM target;
+
+ROLLBACK;
+-- This next SQL statement suceeds, but does nothing since there are
+-- only non-matching rows that do not activate a WHEN clause, so we
+-- provide syntax to just ignore them, rather than allowing data quality
+-- problems
+BEGIN;
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN NOT MATCHED AND s.balance > 100 THEN
+	INSERT VALUES (s.id, s.balance)
+WHEN NOT MATCHED
+	DO NOTHING
+;
+SELECT * FROM target;
+
+ROLLBACK;
+--
+-- Weirdness
+--
+-- MERGE statement containing WHEN clauses that are never executable
+-- NOT an error under the standard
+MERGE into target t
+USING (select * from source) AS s
+ON t.id = s.id
+WHEN MATCHED AND s.balance > 0 THEN
+	UPDATE SET balance = t.balance + s.balance
+WHEN MATCHED THEN
+	DELETE
+WHEN NOT MATCHED THEN
+	INSERT VALUES (s.id, s.balance)
+WHEN NOT MATCHED THEN /* never executed because of order of WHEN clauses */
+	INSERT VALUES (s.id, s.balance + 10)
+WHEN MATCHED THEN /* never executed because of order of WHEN clauses */
+	UPDATE SET balance = t.balance + s.balance
+;