diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 2f33fdb..9f17eca 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -86,7 +86,9 @@ static void intorel_startup(DestReceiver *self, int operation, TupleDesc typeinf
 static void intorel_receive(TupleTableSlot *slot, DestReceiver *self);
 static void intorel_shutdown(DestReceiver *self);
 static void intorel_destroy(DestReceiver *self);
-
+static void ExecMerge(TupleTableSlot * slot,ItemPointer tupleid,	
+						TupleTableSlot * planSlot,DestReceiver * dest,
+						EState * estate);
 /* end of local decls */
 
 
@@ -171,6 +173,7 @@ 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;
 
@@ -795,6 +798,32 @@ InitPlan(QueryDesc *queryDesc, int eflags)
 		i++;
 	}
 
+
+
+
+	/*
+	* for the merge actions, we need to similar things as above
+	*/
+	
+	if(operation == CMD_MERGE)
+	{
+		ListCell *eachact;
+		foreach(eachact, queryDesc->plannedstmt->mergeActPlan)
+		{
+			Plan *actplan = (Plan *)lfirst(eachact);
+			PlanState *actpstate;
+			
+			Assert(IsA(actplan,Plan));
+
+			//here, I call ExecInitNode directly. (correct or not?)
+			actpstate = ExecInitMergeActNode(actplan,estate,0);
+			//replace the plan with this planstate. Still put them in the plannedstmt->mergeActPlan list,
+
+			lfirst(eachact) = actpstate;
+		}
+	}
+	
+
 	/*
 	 * Initialize the private state information for all the nodes in the query
 	 * tree.  This opens files, allocates storage and leaves us ready to start
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index f4cc7d9..cc549ea 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -327,6 +327,54 @@ ExecInitNode(Plan *node, EState *estate, int eflags)
 }
 
 
+/*
+*	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 quals
+*/
+PlanState *
+ExecInitMergeActNode(Plan *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 = node;
+	result->state = estate;
+	
+	/*
+	 * Miscellaneous initialization
+	 *
+	 * create expression context for node
+	 */
+	 
+	ExecAssignExprContext(estate, result);
+
+	/*
+	 * initialize child expressions
+	 */
+	result->targetlist = (List *)
+		ExecInitExpr((Expr *) node->targetlist,  result);
+	result->qual = (List *)
+		ExecInitExpr((Expr *) node->qual, result);
+
+
+	/* Set up instrumentation for this node if requested */
+	if (estate->es_instrument)
+		result->instrument = InstrAlloc(1, estate->es_instrument);
+
+	return result;
+}
+
+
 /* ----------------------------------------------------------------
  *		ExecProcNode
  *
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index 8619ce3..ea0ce87 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -583,6 +583,18 @@ lreplace:;
 }
 
 
+static TupleTableSlot *
+ExecMerge(ItemPointer tupleid,
+		   TupleTableSlot *slot,
+		   TupleTableSlot *planSlot,
+		   EPQState *epqstate,
+		   EState *estate)
+{
+	printf("get a tuple for merge \n");
+	return NULL;
+	
+}
+
 /*
  * Process BEFORE EACH STATEMENT triggers
  */
@@ -603,6 +615,9 @@ 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 +644,9 @@ 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;
@@ -744,6 +762,11 @@ ExecModifyTable(ModifyTableState *node)
 				slot = ExecDelete(tupleid, planSlot,
 								  &node->mt_epqstate, estate);
 				break;
+			case CMD_MERGE:
+				slot = ExecMerge(tupleid, slot, planSlot,
+								  &node->mt_epqstate, estate);
+				break;	
+				
 			default:
 				elog(ERROR, "unknown operation");
 				break;
@@ -955,6 +978,7 @@ ExecInitModifyTable(ModifyTable *node, EState *estate, int eflags)
 				break;
 			case CMD_UPDATE:
 			case CMD_DELETE:
+			case CMD_MERGE:	
 				junk_filter_needed = true;
 				break;
 			default:
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 93dcef5..ff22fa2 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -90,6 +90,7 @@ _copyPlannedStmt(PlannedStmt *from)
 	COPY_NODE_FIELD(relationOids);
 	COPY_NODE_FIELD(invalItems);
 	COPY_SCALAR_FIELD(nParamExec);
+	COPY_NODE_FIELD(mergeActPlan);
 
 	return newnode;
 }
@@ -2273,6 +2274,9 @@ _copyQuery(Query *from)
 	COPY_NODE_FIELD(rowMarks);
 	COPY_NODE_FIELD(setOperations);
 
+	/*merge action list*/
+	COPY_NODE_FIELD(mergeActQry); 
+
 	return newnode;
 }
 
@@ -2343,6 +2347,64 @@ _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 +3964,22 @@ 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..f797f64 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -877,7 +877,7 @@ _equalQuery(Query *a, Query *b)
 	COMPARE_NODE_FIELD(limitCount);
 	COMPARE_NODE_FIELD(rowMarks);
 	COMPARE_NODE_FIELD(setOperations);
-
+	
 	return true;
 }
 
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 79baf4f..dae9f31 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -255,6 +255,7 @@ _outPlannedStmt(StringInfo str, PlannedStmt *node)
 	WRITE_NODE_FIELD(relationOids);
 	WRITE_NODE_FIELD(invalItems);
 	WRITE_INT_FIELD(nParamExec);
+	WRITE_NODE_FIELD(mergeActPlan);
 }
 
 /*
@@ -2019,9 +2020,51 @@ _outQuery(StringInfo str, Query *node)
 	WRITE_NODE_FIELD(limitCount);
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_NODE_FIELD(setOperations);
+	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 +2948,17 @@ _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..04bb60d 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -251,6 +251,25 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	result->invalItems = glob->invalItems;
 	result->nParamExec = list_length(glob->paramlist);
 
+	/*do a simple plan for each actions in the merge command.
+	//put them in mergeActPlan list;
+	*/
+	if(parse->commandType == CMD_MERGE)
+	{
+		ListCell *l;
+
+		
+		foreach(l, parse->mergeActQry)
+		{
+			
+			Plan *actplan = merge_action_planner(glob, (Query *)lfirst(l), NULL,
+								false, tuple_fraction, &root);
+
+			result->mergeActPlan = lappend(result->mergeActPlan, actplan);
+		}
+
+	}
+
 	return result;
 }
 
@@ -584,6 +603,74 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	return plan;
 }
 
+
+
+Plan *
+merge_action_planner(PlannerGlobal *glob, Query *parse,
+				 PlannerInfo *parent_root,
+				 bool hasRecursion, double tuple_fraction,
+				 PlannerInfo **subroot)
+{
+	PlannerInfo *root;
+	Plan	   *plan;
+	
+	
+
+	/* 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.
+	 */
+	if (parse->resultRelation &&
+		rt_fetch(parse->resultRelation, parse->rtable)->inh)
+		plan = inheritance_planner(root);
+	else
+		plan = grouping_planner(root, tuple_fraction);
+
+	
+	return plan;
+}
+
+
 /*
  * 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..adf8795 100644
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -84,7 +84,7 @@ preprocess_targetlist(PlannerInfo *root, List *tlist)
 	 * delete.	This extra field is marked "junk" so that it is not stored
 	 * back into the tuple.
 	 */
-	if (command_type == CMD_UPDATE || command_type == CMD_DELETE)
+	if (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..8c6af99 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 +291,32 @@ 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;
 
+
 	/*
-	 * 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);
@@ -347,6 +366,8 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 	 * 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 +403,8 @@ 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 */
@@ -1730,17 +1752,19 @@ 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);
-
-	/*
-	 * 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);
 
 	qual = transformWhereClause(pstate, stmt->whereClause, "WHERE");
@@ -2241,3 +2265,336 @@ 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..5567188 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 +1900,131 @@ 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/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/executor.h b/src/include/executor/executor.h
index 9fe6e4c..8b75855 100644
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -194,6 +194,7 @@ extern DestReceiver *CreateIntoRelDestReceiver(void);
  * prototypes from functions in execProcnode.c
  */
 extern PlanState *ExecInitNode(Plan *node, EState *estate, int eflags);
+extern PlanState *ExecInitMergeActNode(Plan *node, EState *estate, int eflags);
 extern TupleTableSlot *ExecProcNode(PlanState *node);
 extern Node *MultiExecProcNode(PlanState *node);
 extern void ExecEndNode(PlanState *node);
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index a5f5df5..38bea7c 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -261,6 +261,15 @@ 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 +520,7 @@ 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..392d7f7 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -146,6 +146,9 @@ typedef struct Query
 
 	Node	   *setOperations;	/* set-operation tree if this is top level of
 								 * a UNION/INTERSECT/EXCEPT query */
+
+	List 		*mergeActQry; /* the list of all the merge actions. 
+								* used only for merge query statment*/							 
 } Query;
 
 
@@ -990,6 +993,30 @@ 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..236b0c7 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -66,6 +66,9 @@ typedef struct PlannedStmt
 	List	   *invalItems;		/* other dependencies, as PlanInvalItems */
 
 	int			nParamExec;		/* number of PARAM_EXEC Params used */
+
+	List 		*mergeActPlan;  /*the plans for merge actions*/
+	
 } PlannedStmt;
 
 /* macro for fetching the Plan associated with a SubPlan node */
diff --git a/src/include/optimizer/planner.h b/src/include/optimizer/planner.h
index 805dee7..ae705ec 100644
--- a/src/include/optimizer/planner.h
+++ b/src/include/optimizer/planner.h
@@ -34,6 +34,10 @@ extern Plan *subquery_planner(PlannerGlobal *glob, Query *parse,
 				 PlannerInfo *parent_root,
 				 bool hasRecursion, double tuple_fraction,
 				 PlannerInfo **subroot);
+extern Plan *merge_action_planner(PlannerGlobal *glob, Query *parse,
+				 PlannerInfo *parent_root,
+				 bool hasRecursion, double tuple_fraction,
+				 PlannerInfo **subroot);
 
 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);