diff --git a/doc/src/sgml/ref/allfiles.sgml b/doc/src/sgml/ref/allfiles.sgml
index 7518c84..3aa9aab 100644
--- a/doc/src/sgml/ref/allfiles.sgml
+++ b/doc/src/sgml/ref/allfiles.sgml
@@ -119,6 +119,7 @@ Complete list of usable sgml source files in this directory.
 <!entity listen             system "listen.sgml">
 <!entity load               system "load.sgml">
 <!entity lock               system "lock.sgml">
+<!entity merge              system "merge.sgml">
 <!entity move               system "move.sgml">
 <!entity notify             system "notify.sgml">
 <!entity prepare            system "prepare.sgml">
diff --git a/doc/src/sgml/ref/merge.sgml b/doc/src/sgml/ref/merge.sgml
new file mode 100644
index 0000000..7c73623
--- /dev/null
+++ b/doc/src/sgml/ref/merge.sgml
@@ -0,0 +1,409 @@
+<!--
+$PostgreSQL$
+-->
+
+<refentry id="SQL-MERGE">
+ <refmeta>
+  <refentrytitle id="SQL-MERGE-TITLE">MERGE</refentrytitle>
+  <refmiscinfo>SQL - Language Statements</refmiscinfo>
+ </refmeta>
+
+ <refnamediv>
+  <refname>MERGE</refname>
+  <refpurpose>update, insert or delete rows of a table based upon source data</refpurpose>
+ </refnamediv>
+
+ <indexterm zone="sql-merge">
+  <primary>MERGE</primary>
+ </indexterm>
+
+ <refsynopsisdiv>
+<synopsis>
+MERGE INTO <replaceable class="PARAMETER">table</replaceable> [ [ AS ] <replaceable class="parameter">alias</replaceable> ]
+USING <replaceable class="PARAMETER">source-query</replaceable>
+ON <replaceable class="PARAMETER">join_condition</replaceable>
+[<replaceable class="PARAMETER">when_clause</replaceable> [...]]
+
+where <replaceable class="PARAMETER">when_clause</replaceable> is
+
+{ WHEN MATCHED [ AND <replaceable class="PARAMETER">condition</replaceable> ] THEN { <replaceable class="PARAMETER">merge_update</replaceable> | DELETE | DO NOTHING | RAISE ERROR}
+  WHEN NOT MATCHED [ AND <replaceable class="PARAMETER">condition</replaceable> ] THEN { <replaceable class="PARAMETER">merge_insert</replaceable> | DO NOTHING | RAISE ERROR} }
+
+where <replaceable class="PARAMETER">merge_update</replaceable> is
+
+UPDATE SET { <replaceable class="PARAMETER">column</replaceable> = { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } |
+           ( <replaceable class="PARAMETER">column</replaceable> [, ...] ) = ( { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...] ) } [, ...]
+
+and <replaceable class="PARAMETER">merge_insert</replaceable> is
+
+INSERT [( <replaceable class="PARAMETER">column</replaceable> [, ...] )] { VALUES ( { <replaceable class="PARAMETER">expression</replaceable> | DEFAULT } [, ...] ) | DEFAULT VALUES }
+</synopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+  <title>Description</title>
+
+  <para>
+   <command>MERGE</command> performs at most one action on each row from
+   the target table, driven by the rows from the source query. This
+   provides a way to specify a single SQL statement that can conditionally
+   <command>UPDATE</command> or <command>INSERT</command> rows, a task
+   that would otherwise require multiple procedural language statements.
+  </para>
+
+  <para>
+   First, the <command>MERGE</command> command performs a left outer join
+   from source query to target table, producing zero or more merged rows. For
+   each merged row, <literal>WHEN</> clauses are evaluated in the
+   specified order until one of them is activated. The corresponding action
+   is then applied and processing continues for the next row.
+  </para>
+
+  <para>
+   <command>MERGE</command> actions have the same effect as
+   regular <command>UPDATE</command>, <command>INSERT</command>, or
+   <command>DELETE</command> commands of the same names, though the syntax
+   is slightly different.
+  </para>
+
+  <para>
+   If no <literal>WHEN</> clause activates then an implicit action of
+   <literal>RAISE ERROR</> is performed for that row. If that
+   implicit action is not desirable an explicit action of
+   <literal>DO NOTHING</> may be specified instead.
+  </para>
+
+  <para>
+   <command>MERGE</command> will only affect rows only in the specified table.
+  </para>
+
+  <para>
+   There is no <literal>RETURNING</> clause with <command>MERGE</command>.
+  </para>
+
+  <para>
+   There is no MERGE privilege.
+   You must have the <literal>UPDATE</literal> privilege on the table
+   if you specify an update action, the <literal>INSERT</literal> privilege if
+   you specify an insert action and/or the <literal>DELETE</literal> privilege
+   if you wish to delete. You will also require the
+   <literal>SELECT</literal> privilege to any table whose values are read
+   in the <replaceable class="parameter">expressions</replaceable> or
+   <replaceable class="parameter">condition</replaceable>.
+  </para>
+ </refsect1>
+
+ <refsect1>
+  <title>Parameters</title>
+
+  <variablelist>
+   <varlistentry>
+    <term><replaceable class="PARAMETER">table</replaceable></term>
+    <listitem>
+     <para>
+      The name (optionally schema-qualified) of the table to merge into.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">alias</replaceable></term>
+    <listitem>
+     <para>
+      A substitute name for the target table. When an alias is
+      provided, it completely hides the actual name of the table.  For
+      example, given <literal>MERGE foo AS f</>, the remainder of the
+      <command>MERGE</command> statement must refer to this table as
+      <literal>f</> not <literal>foo</>.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="PARAMETER">source-query</replaceable></term>
+    <listitem>
+     <para>
+      A query (<command>SELECT</command> statement or <command>VALUES</command>
+      statement) that supplies the rows to be merged into the target table.
+      Refer to the <xref linkend="sql-select">
+      statement or <xref linkend="sql-values">
+      statement for a description of the syntax.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="PARAMETER">join_condition</replaceable></term>
+    <listitem>
+     <para>
+      <replaceable class="parameter">join_condition</replaceable> is
+      an expression resulting in a value of type
+      <type>boolean</type> (similar to a <literal>WHERE</literal>
+      clause) that specifies which rows in the join are considered to
+      match.  You should ensure that the join produces at most one output
+      row for each row to be modified.  An attempt to modify any row of the
+      target table more than once will result in an error.  This behaviour
+      requires the user to take greater care in using <command>MERGE</command>,
+      though is required explicitly by the SQL Standard.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="PARAMETER">condition</replaceable></term>
+    <listitem>
+     <para>
+      An expression that returns a value of type <type>boolean</type>.
+      If this expression returns <literal>true</> then the <literal>WHEN</>
+	  clause will be activated and the corresponding action will occur for
+      that row.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="PARAMETER">merge_update</replaceable></term>
+    <listitem>
+     <para>
+      The specification of an <literal>UPDATE</> action.  Do not include
+      the table name, as you would normally do with an
+      <xref linkend="sql-update"> command.
+      For example, <literal>UPDATE tab SET col = 1</> is invalid. Also,
+      do not include a <literal>WHERE</> clause, since only the current
+      can be updated. For example,
+      <literal>UPDATE SET col = 1 WHERE key = 57</> is invalid.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="PARAMETER">merge_insert</replaceable></term>
+    <listitem>
+     <para>
+      The specification of an <literal>INSERT</> action.  Do not include
+      the table name, as you would normally do with an
+      <xref linkend="sql-insert"> command.
+      For example, <literal>INSERT INTO tab VALUES (1, 50)</> is invalid.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="PARAMETER">column</replaceable></term>
+    <listitem>
+     <para>
+      The name of a column in <replaceable
+      class="PARAMETER">table</replaceable>.
+      The column name can be qualified with a subfield name or array
+      subscript, if needed.  Do not include the table's name in the
+      specification of a target column &mdash; for example,
+      <literal>UPDATE SET tab.col = 1</> is invalid.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="PARAMETER">expression</replaceable></term>
+    <listitem>
+     <para>
+      An expression to assign to the column.  The expression can use the
+      old values of this and other columns in the table.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><literal>DEFAULT</literal></term>
+    <listitem>
+     <para>
+      Set the column to its default value (which will be NULL if no
+      specific default expression has been assigned to it).
+     </para>
+    </listitem>
+   </varlistentry>
+
+  </variablelist>
+ </refsect1>
+
+ <refsect1>
+  <title>Outputs</title>
+
+  <para>
+   On successful completion, a <command>MERGE</> command returns a command
+   tag of the form
+<screen>
+MERGE <replaceable class="parameter">total-count</replaceable>
+</screen>
+   The <replaceable class="parameter">total-count</replaceable> is the number
+   of rows changed (either updated, inserted or deleted).
+   If <replaceable class="parameter">total-count</replaceable> is 0, no rows
+   were changed (this is not considered an error).
+  </para>
+
+  <para>
+   The number of rows updated, inserted or deleted is not available as part
+   of the command tag. An optional NOTIFY message can be generated to
+   present this information, if desired.
+<screen>
+NOTIFY:  34 rows processed: 11 updated, 5 deleted, 15 inserted, 3 default inserts, 0 no action
+</screen>
+  </para>
+
+ </refsect1>
+
+ <refsect1>
+  <title>Notes</title>
+
+  <para>
+   What essentially happens is that the target table is left outer-joined to
+   the tables mentioned in the <replaceable>source-query</replaceable>, and
+   each output row of the join may then activate at most one when-clause.
+   The row will be matched only once per statement, so the status of
+   <literal>MATCHED</> or <literal>NOT MATCHED</> cannot change once testing
+   of <literal>WHEN</> clauses has begun. <command>MERGE</command> will not
+   invoke Rules.
+  </para>
+
+  <para>
+   The following steps take place during the execution of
+   <command>MERGE</command>.
+    <orderedlist>
+     <listitem>
+      <para>
+       Perform any BEFORE STATEMENT triggers for actions specified, whether or
+       not they actually occur.
+      </para>
+     </listitem>
+     <listitem>
+      <para>
+       Perform left outer join from source to target table. Then for each row:
+       <orderedlist>
+        <listitem>
+         <para>
+          Evaluate whether each row is MATCHED or NOT MATCHED.
+         </para>
+        </listitem>
+        <listitem>
+         <para>
+          Test each WHEN condition in the order specified until one activates.
+          Identify the action and its event type.
+         </para>
+        </listitem>
+        <listitem>
+         <para>
+          Perform any BEFORE ROW triggers that fire for the action's event type.
+         </para>
+        </listitem>
+        <listitem>
+         <para>
+          Apply the action specified.
+         </para>
+        </listitem>
+        <listitem>
+         <para>
+          Perform any AFTER ROW triggers that fire for the action's event type.
+         </para>
+        </listitem>
+       </orderedlist>
+      </para>
+     </listitem>
+     <listitem>
+      <para>
+       Perform any AFTER STATEMENT triggers for actions specified, whether or
+       not they actually occur.
+      </para>
+     </listitem>
+    </orderedlist>
+   In summary, statement triggers for an event type (say, INSERT) will
+   be fired whenever we <emphasis>specify</> an action of that kind. Row-level
+   triggers will fire only for event type <emphasis>activated</>.
+   So a <command>MERGE</command> might fire statement triggers for both
+   <literal>UPDATE</> and <literal>INSERT</>, even though only
+   <literal>UPDATE</> row triggers were fired.
+  </para>
+
+ </refsect1>
+
+ <refsect1>
+  <title>Examples</title>
+
+  <para>
+   Attempt to insert a new stock item along with the quantity of stock. If
+   the item already exists, instead update the stock count of the existing
+   item.
+<programlisting>
+MERGE INTO wines w
+USING (VALUES('Chateau Lafite 2003', '24')) v
+ON v.column1 = w.winename
+WHEN NOT MATCHED THEN
+  INSERT VALUES(v.column1, v.column2)
+WHEN MATCHED THEN
+  UPDATE SET stock = stock + v.column2;
+</programlisting>
+  </para>
+
+  <para>
+   Perform maintenance on CustomerAccounts based upon new Transactions.
+   The following statement will fail if any accounts have had more than
+   one transaction
+
+<programlisting>
+MERGE CustomerAccount CA
+
+USING (SELECT CustomerId, TransactionValue,
+       FROM Transactions
+       WHERE TransactionId > 35345678) AS T
+
+ON T.CustomerId = CA.CustomerId
+
+WHEN MATCHED THEN
+  UPDATE SET Balance = Balance - TransactionValue
+
+WHEN NOT MATCHED THEN
+  INSERT (CustomerId, Balance)
+  VALUES (T.CustomerId, T.TransactionValue)
+;
+</programlisting>
+
+   so the right way to do this is to pre-aggregate the data
+
+<programlisting>
+MERGE CustomerAccount CA
+
+USING (SELECT CustomerId, Sum(TransactionValue) As TransactionSum
+       FROM Transactions
+       WHERE TransactionId > 35345678
+       GROUP BY CustomerId) AS T
+
+ON T.CustomerId = CA.CustomerId
+
+WHEN MATCHED THEN
+  UPDATE SET Balance = Balance - TransactionSum
+
+WHEN NOT MATCHED THEN
+  INSERT (CustomerId, Balance)
+  VALUES (T.CustomerId, T.TransactionSum)
+;
+</programlisting>
+  </para>
+
+ </refsect1>
+
+ <refsect1>
+  <title>Compatibility</title>
+
+  <para>
+   This command conforms to the <acronym>SQL</acronym> standard, except
+   that the <literal>DELETE</literal> and <literal>DO NOTHING</> actions
+   are <productname>PostgreSQL</productname> extensions.
+  </para>
+
+  <para>
+   According to the standard, the column-list syntax for an <literal>UPDATE</>
+   action should allow a list of columns to be assigned from a single
+   row-valued expression.
+   This is not currently implemented &mdash; the source must be a list
+   of independent expressions.
+  </para>
+ </refsect1>
+</refentry>
diff --git a/doc/src/sgml/ref/update.sgml b/doc/src/sgml/ref/update.sgml
index 5268794..677390c 100644
--- a/doc/src/sgml/ref/update.sgml
+++ b/doc/src/sgml/ref/update.sgml
@@ -327,6 +327,9 @@ UPDATE wines SET stock = stock + 24 WHERE winename = 'Chateau Lafite 2003';
 -- continue with other operations, and eventually
 COMMIT;
 </programlisting>
+
+    This operation can be executed in a single statement using
+    <xref linkend="sql-merge" endterm="sql-merge-title">.
   </para>
 
   <para>
diff --git a/doc/src/sgml/reference.sgml b/doc/src/sgml/reference.sgml
index c33d883..5068235 100644
--- a/doc/src/sgml/reference.sgml
+++ b/doc/src/sgml/reference.sgml
@@ -147,6 +147,7 @@
    &listen;
    &load;
    &lock;
+   &merge;
    &move;
    &notify;
    &prepare;
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index fcb20d6..f84e9dd 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -76,6 +76,8 @@ 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);
@@ -639,6 +641,9 @@ ExplainNode(PlanState *planstate, List *ancestors,
 				case CMD_DELETE:
 					pname = operation = "Delete";
 					break;
+				case CMD_MERGE:
+					pname = operation = "Merge";
+					break;
 				default:
 					pname = "???";
 					break;
@@ -1194,6 +1199,11 @@ ExplainNode(PlanState *planstate, List *ancestors,
 	if (innerPlanState(planstate))
 		ExplainNode(innerPlanState(planstate), ancestors,
 					"Inner", NULL, es);
+	
+	if (IsA(plan, ModifyTable) && 
+				((ModifyTable *)plan)->operation == CMD_MERGE)
+			ExplainMergeActions((ModifyTableState *) planstate,
+										ancestors, es);
 
 	/* special child plans */
 	switch (nodeTag(plan))
@@ -1504,6 +1514,89 @@ explain_get_index_name(Oid indexId)
 	return result;
 }
 
+static void
+ExplainMergeActions(ModifyTableState *mt_planstate, List *ancestors,
+					ExplainState *es)
+{
+	ListCell *l;
+	int actno = 1;
+	StringInfo buf = makeStringInfo();
+	StringInfo acttitle = makeStringInfo();
+	MergeActionSet *actset;
+
+	if (mt_planstate->operation != CMD_MERGE ||
+		mt_planstate->mt_mergeActPstates == NIL)
+		return;
+
+	actset = mt_planstate->mt_mergeActPstates[0];
+
+	foreach(l, actset->actions)
+	{
+		ModifyTableState *mt_state = (ModifyTableState *) lfirst(l);
+		MergeActionState *act_pstate = (MergeActionState *) mt_state->mt_plans[0];
+		MergeAction *act_plan = (MergeAction *) act_pstate->ps.plan;
+
+		/*prepare the title*/
+		resetStringInfo(acttitle);
+		appendStringInfo(acttitle, "Action %d", actno);
+
+		/*prepare the string for printing*/
+		resetStringInfo(buf);
+		switch(act_pstate->operation)
+		{
+			case CMD_INSERT:
+				appendStringInfoString(buf, "Insert When ");
+				break;
+			case CMD_UPDATE:
+				appendStringInfoString(buf, "Update When ");
+				break;
+			case CMD_DELETE:
+				appendStringInfoString(buf, "Delete When ");
+				break;
+			case CMD_DONOTHING:
+				appendStringInfoString(buf, "Do Nothing When ");
+				break;
+			default:
+				elog(ERROR, "unknown merge action");
+		}
+
+		if (act_plan->matched)
+			appendStringInfoString(buf, "Matched ");
+		else
+			appendStringInfoString(buf, "Not Mactched ");
+
+		if (act_plan->flattenedqual)
+			appendStringInfoString(buf, "And ");
+
+		/*print the action type*/
+		ExplainPropertyText(acttitle->data, buf->data, es);
+
+		/*print the action qual*/	
+		show_qual(act_plan->flattenedqual, "Qual",
+				  &act_pstate->ps, ancestors, true, es);
+
+		/*print the target list of action*/
+		if (es->verbose &&
+			(act_plan->operation == CMD_INSERT || 
+			act_plan->operation == CMD_UPDATE))
+		{
+			List *orignialtlist;
+			
+			orignialtlist = act_plan->plan.targetlist;
+			act_plan->plan.targetlist = act_plan->flattenedtlist;
+			show_plan_tlist((PlanState *) act_pstate, ancestors, es);
+			act_plan->plan.targetlist = orignialtlist;
+		}
+
+		if (act_pstate->ps.subPlan)
+			ExplainSubPlans(act_pstate->ps.subPlan, ancestors, "SubPlan", es);
+
+		actno++;
+	}
+
+	ExplainPropertyText("MainPlan", "", es);
+}
+
 /*
  * Show the target of a Scan node
  */
diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index e3230d4..890fa82 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -2342,6 +2342,87 @@ ExecASTruncateTriggers(EState *estate, ResultRelInfo *relinfo)
 							  false, NULL, NULL, NIL, NULL);
 }
 
+void
+ExecBSMergeTriggers(ModifyTableState *mt_state)
+{
+	ListCell *l;
+	MergeActionSet *actset;
+	bool doUpdateTriggers = false;
+	bool doInsertTriggers = false;
+	bool doDeleteTriggers = false;
+
+	/* Scan the actions to see what kind of statements there is */
+	actset = mt_state->mt_mergeActPstates[0];
+	foreach(l, actset->actions)
+	{
+		ModifyTableState *actmtstate;
+		MergeActionState *actPstate;
+		MergeAction *actplan;
+
+		actmtstate = (ModifyTableState *) lfirst(l);
+		actPstate = (MergeActionState *) actmtstate->mt_plans[0];
+		actplan = (MergeAction *) actPstate->ps.plan;
+
+		if (actplan->operation == CMD_UPDATE)
+			doUpdateTriggers = true;
+		else if (actplan->operation == CMD_INSERT)
+			doInsertTriggers = true;
+		else if (actplan->operation == CMD_DELETE)
+			doDeleteTriggers = true;
+	}
+
+	/* And fire the triggers */
+	if (doUpdateTriggers)
+		ExecBSUpdateTriggers(mt_state->ps.state,
+							 mt_state->ps.state->es_result_relations);
+	if (doInsertTriggers)
+		ExecBSInsertTriggers(mt_state->ps.state,
+							 mt_state->ps.state->es_result_relations);
+	if (doDeleteTriggers)
+		ExecBSDeleteTriggers(mt_state->ps.state,
+							 mt_state->ps.state->es_result_relations);
+}
+
+void
+ExecASMergeTriggers(ModifyTableState *mt_state)
+{
+	ListCell *l;
+	MergeActionSet *actset;
+	bool doUpdateTriggers = false;
+	bool doInsertTriggers = false;
+	bool doDeleteTriggers = false;
+
+	/* Scan the actions to see what kind of statements there is */
+	actset = mt_state->mt_mergeActPstates[0];
+	foreach(l, actset->actions)
+	{
+		ModifyTableState *actmtstate;
+		MergeActionState *actPstate;
+		MergeAction *actplan;
+
+		actmtstate = (ModifyTableState *)lfirst(l);
+		actPstate = (MergeActionState *)actmtstate->mt_plans[0];
+		actplan = (MergeAction *)actPstate->ps.plan;
+
+		if(actplan->operation == CMD_UPDATE)
+			doUpdateTriggers = true;
+		else if(actplan->operation == CMD_INSERT)
+			doInsertTriggers = true;
+		else if(actplan->operation == CMD_DELETE)
+			doDeleteTriggers = true;
+	}
+
+	/* And fire the triggers */
+	if (doUpdateTriggers)
+		ExecASUpdateTriggers(mt_state->ps.state,
+							 mt_state->ps.state->es_result_relations);
+	if (doInsertTriggers)
+		ExecASInsertTriggers(mt_state->ps.state,
+							 mt_state->ps.state->es_result_relations);
+	if (doDeleteTriggers)
+		ExecASDeleteTriggers(mt_state->ps.state,
+							 mt_state->ps.state->es_result_relations);
+}
 
 static HeapTuple
 GetTupleForTrigger(EState *estate,
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index b34a154..2b7ceb1 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..ff691c7 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 562c419..bede096 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -582,6 +582,103 @@ lreplace:;
 	return NULL;
 }
 
+static TupleTableSlot *
+ExecMerge(ItemPointer tupleid,
+		   TupleTableSlot *slot,
+		   TupleTableSlot *planSlot,
+		   MergeActionSet *actset,
+		   EState *estate)
+{
+
+	TupleTableSlot *actslot = NULL;
+	ListCell *each;
+
+	/*
+	 * Try the merge actions one by one until we have a match.
+	 */
+	foreach(each, actset->actions)
+	{
+		ModifyTableState *mt_pstate;
+		MergeActionState *action_pstate;
+		ExprContext *econtext;
+		bool matched;
+
+		mt_pstate = (ModifyTableState *) lfirst(each);
+		Assert(IsA(mt_pstate, ModifyTableState));
+
+		/*
+		 * mt_pstate is supposed to have only ONE mt_plans,
+		 * which is a MergeActionState
+		 */
+		action_pstate = (MergeActionState *) mt_pstate->mt_plans[0];
+		matched = ((MergeAction *)action_pstate->ps.plan)->matched;
+
+		/*
+		 * If tupleid == NULL, it is a NOT MATCHED case,
+		 * else, it is a MATCHED case,
+		 */
+		if ((tupleid == NULL && matched) || 
+			(tupleid != NULL && !matched))
+			continue;
+
+		/* Setup the expression context. */
+		econtext = action_pstate->ps.ps_ExprContext;
+
+		/*
+		 * Check that additional quals match, if any.
+		 */
+		if (action_pstate->ps.qual)
+		{
+			ResetExprContext(econtext);
+
+			econtext->ecxt_scantuple = slot;
+			econtext->ecxt_outertuple = planSlot;
+
+			if (!ExecQual(action_pstate->ps.qual, econtext, false))
+				continue;
+		}
+
+		/* Ok, we have a match. Perform the action */
+
+		/* First project any RETURNING result tuple slot, if needed */
+		if (action_pstate->operation == CMD_INSERT ||
+			action_pstate->operation == CMD_UPDATE)
+			actslot = ExecProcessReturning(action_pstate->ps.ps_ProjInfo,
+										   slot, planSlot);
+
+		switch (action_pstate->operation)
+		{
+			case CMD_INSERT:
+				return ExecInsert(actslot, planSlot, estate);
+
+			case CMD_UPDATE:
+				return ExecUpdate(tupleid,
+								  actslot,
+								  planSlot,
+								  &mt_pstate->mt_epqstate,
+								  estate);
+
+			case CMD_DELETE:
+				return ExecDelete(tupleid,
+								  planSlot,
+								  &mt_pstate->mt_epqstate,
+								  estate);
+
+			case CMD_DONOTHING:
+				return NULL;
+
+			default:
+				elog(ERROR, "unknown merge action type for execute");
+				break;
+		}
+	}
+
+	/*
+	 * No matching action found. Perform the default action, which is
+	 * DO NOTHING.
+	 */
+	return NULL;
+}
 
 /*
  * Process BEFORE EACH STATEMENT triggers
@@ -603,6 +700,9 @@ fireBSTriggers(ModifyTableState *node)
 			ExecBSDeleteTriggers(node->ps.state,
 								 node->ps.state->es_result_relations);
 			break;
+		case CMD_MERGE:
+			ExecBSMergeTriggers(node);
+			break;
 		default:
 			elog(ERROR, "unknown operation");
 			break;
@@ -629,6 +729,9 @@ fireASTriggers(ModifyTableState *node)
 			ExecASDeleteTriggers(node->ps.state,
 								 node->ps.state->es_result_relations);
 			break;
+		case CMD_MERGE:
+			ExecASMergeTriggers(node);
+			break;
 		default:
 			elog(ERROR, "unknown operation");
 			break;
@@ -654,6 +757,7 @@ ExecModifyTable(ModifyTableState *node)
 	TupleTableSlot *planSlot;
 	ItemPointer tupleid = NULL;
 	ItemPointerData tuple_ctid;
+	MergeActionSet *mergeActSet = NULL;
 
 	/*
 	 * On first call, fire BEFORE STATEMENT triggers before proceeding.
@@ -675,6 +779,8 @@ ExecModifyTable(ModifyTableState *node)
 	/* Preload local variables */
 	subplanstate = node->mt_plans[node->mt_whichplan];
 	junkfilter = estate->es_result_relation_info->ri_junkFilter;
+	if(node->mt_mergeActPstates)
+		mergeActSet = node->mt_mergeActPstates[node->mt_whichplan];
 
 	/*
 	 * Fetch rows from subplan(s), and execute the required table modification
@@ -701,6 +807,8 @@ ExecModifyTable(ModifyTableState *node)
 				estate->es_result_relation_info++;
 				subplanstate = node->mt_plans[node->mt_whichplan];
 				junkfilter = estate->es_result_relation_info->ri_junkFilter;
+				if(node->mt_mergeActPstates)
+					mergeActSet = node->mt_mergeActPstates[node->mt_whichplan];
 				EvalPlanQualSetPlan(&node->mt_epqstate, subplanstate->plan);
 				continue;
 			}
@@ -716,20 +824,32 @@ 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");
+				{
+					/*
+					 * Shouldn't ever get a null result for UPDATE or DELETE.
+					 * MERGE gets 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;
+					tupleid = (ItemPointer) DatumGetPointer(datum);
+					tuple_ctid = *tupleid;	/* be sure we don't free the ctid!! */
+					tupleid = &tuple_ctid;
+				}
 			}
 
 			/*
@@ -752,6 +872,10 @@ ExecModifyTable(ModifyTableState *node)
 				slot = ExecDelete(tupleid, planSlot,
 								  &node->mt_epqstate, estate);
 				break;
+			case CMD_MERGE:
+				slot = ExecMerge(tupleid, slot, planSlot,
+								 mergeActSet, estate);
+				break;
 			default:
 				elog(ERROR, "unknown operation");
 				break;
@@ -779,6 +903,69 @@ ExecModifyTable(ModifyTableState *node)
 	return NULL;
 }
 
+/*
+ *	When init a merge plan, we also need init its action plans.
+ *	These action plans are "MergeAction" plans.
+ *
+ *	This function mainly handles 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);
+
+	/*
+	 * XXX: do we need a check for the plan output here ?
+	 * (by calling the ExecCheckPlanOutput() function
+	 */
+
+	return result;
+}
+
 /* ----------------------------------------------------------------
  *		ExecInitModifyTable
  * ----------------------------------------------------------------
@@ -794,6 +981,7 @@ 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)));
@@ -834,6 +1022,16 @@ 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 junkfilter.
+		 *	junkfilter 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++;
@@ -963,7 +1161,11 @@ 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;
+			case CMD_DONOTHING:
 				break;
 			default:
 				elog(ERROR, "unknown operation");
@@ -986,9 +1188,10 @@ 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");
@@ -1014,6 +1217,36 @@ 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 do similar things as above.
+	 *Each action in each action set should be init by the ExecInitNode.
+	 *The returned planstates will take the place of the original plan nodes.
+	 *These new action set will be put in the mt_mergeActPstates array.
+	 */
+	if(node->operation == CMD_MERGE)
+	{
+		/*we have one action set for each result relation (main plan)*/
+		mtstate->mt_mergeActPstates = 
+			(MergeActionSet **) palloc0(sizeof(MergeActionSet*) * nplans);
+
+		estate->es_result_relation_info = estate->es_result_relations;
+		i = 0;
+		foreach(l, node->mergeActPlan)
+		{
+			ListCell *e;
+			MergeActionSet *actset = (MergeActionSet *) lfirst(l);
+
+			foreach(e, actset->actions)
+			{
+				lfirst(e) = ExecInitNode((Plan *)lfirst(e),  estate, 0);
+			}		
+			mtstate->mt_mergeActPstates[i] = actset;
+			estate->es_result_relation_info++;
+			i++;
+		}
+		estate->es_result_relation_info = NULL;
+	}
+
 	return mtstate;
 }
 
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 87de0c5..3ff2dce 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -177,6 +177,42 @@ _copyModifyTable(ModifyTable *from)
 	COPY_NODE_FIELD(returningLists);
 	COPY_NODE_FIELD(rowMarks);
 	COPY_SCALAR_FIELD(epqParam);
+	COPY_NODE_FIELD(mergeActPlan);
+
+	return newnode;
+}
+
+/*
+ * _copyMergeAction
+ */
+static MergeAction *
+_copyMergeAction(MergeAction *from)
+{
+	MergeAction *newnode = makeNode(MergeAction);
+
+	/*
+	 * copy node superclass fields
+	 */
+	CopyPlanFields((Plan *) from, (Plan *) newnode);
+
+	COPY_SCALAR_FIELD(operation);	
+	COPY_SCALAR_FIELD(matched);
+	COPY_NODE_FIELD(flattenedqual);
+	COPY_NODE_FIELD(flattenedtlist);
+
+	return newnode;
+}
+
+/*
+ * _copyMergeActionSet
+ */
+static MergeActionSet *
+_copyMergeActionSet(MergeActionSet *from)
+{
+	MergeActionSet *newnode = makeNode(MergeActionSet);
+
+	COPY_SCALAR_FIELD(result_relation);
+	COPY_NODE_FIELD(actions);
 
 	return newnode;
 }
@@ -2274,6 +2310,10 @@ _copyQuery(Query *from)
 	COPY_NODE_FIELD(rowMarks);
 	COPY_NODE_FIELD(setOperations);
 	COPY_NODE_FIELD(constraintDeps);
+	COPY_SCALAR_FIELD(isMergeAction);
+	COPY_SCALAR_FIELD(matched);
+	COPY_SCALAR_FIELD(sourceAttrNo);
+	COPY_NODE_FIELD(mergeActQry);
 
 	return newnode;
 }
@@ -2283,6 +2323,7 @@ _copyInsertStmt(InsertStmt *from)
 {
 	InsertStmt *newnode = makeNode(InsertStmt);
 
+	COPY_SCALAR_FIELD(isMergeAction);
 	COPY_NODE_FIELD(relation);
 	COPY_NODE_FIELD(cols);
 	COPY_NODE_FIELD(selectStmt);
@@ -2296,6 +2337,7 @@ _copyDeleteStmt(DeleteStmt *from)
 {
 	DeleteStmt *newnode = makeNode(DeleteStmt);
 
+	COPY_SCALAR_FIELD(isMergeAction);
 	COPY_NODE_FIELD(relation);
 	COPY_NODE_FIELD(usingClause);
 	COPY_NODE_FIELD(whereClause);
@@ -2309,6 +2351,7 @@ _copyUpdateStmt(UpdateStmt *from)
 {
 	UpdateStmt *newnode = makeNode(UpdateStmt);
 
+	COPY_SCALAR_FIELD(isMergeAction);
 	COPY_NODE_FIELD(relation);
 	COPY_NODE_FIELD(targetList);
 	COPY_NODE_FIELD(whereClause);
@@ -2345,6 +2388,47 @@ _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 MergeDoNothing *
+_copyMergeDoNothing(MergeDoNothing *from)
+{
+	MergeDoNothing *newnode = makeNode(MergeDoNothing);
+
+	return newnode;
+}
+
+static MergeError*
+_copyMergeError(MergeError *from)
+{
+	MergeError *newnode = makeNode(MergeError);
+
+	return newnode;
+}
+
 static SetOperationStmt *
 _copySetOperationStmt(SetOperationStmt *from)
 {
@@ -3607,6 +3691,12 @@ copyObject(void *from)
 		case T_ModifyTable:
 			retval = _copyModifyTable(from);
 			break;
+		case T_MergeAction:
+			retval = _copyMergeAction(from);
+			break;
+		case T_MergeActionSet:
+			retval = _copyMergeActionSet(from);
+			break;
 		case T_Append:
 			retval = _copyAppend(from);
 			break;
@@ -3907,6 +3997,18 @@ 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_MergeDoNothing:
+			retval = _copyMergeDoNothing(from);
+			break;
+		case T_MergeError:
+			retval = _copyMergeError(from);
+			break;
 		case T_SetOperationStmt:
 			retval = _copySetOperationStmt(from);
 			break;
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 6f6e9e4..4d0d7c3 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -878,6 +878,10 @@ _equalQuery(Query *a, Query *b)
 	COMPARE_NODE_FIELD(rowMarks);
 	COMPARE_NODE_FIELD(setOperations);
 	COMPARE_NODE_FIELD(constraintDeps);
+	COMPARE_SCALAR_FIELD(isMergeAction);
+	COMPARE_SCALAR_FIELD(matched);
+	COMPARE_SCALAR_FIELD(sourceAttrNo);
+	COMPARE_NODE_FIELD(mergeActQry);
 
 	return true;
 }
@@ -885,6 +889,7 @@ _equalQuery(Query *a, Query *b)
 static bool
 _equalInsertStmt(InsertStmt *a, InsertStmt *b)
 {
+	COMPARE_SCALAR_FIELD(isMergeAction);
 	COMPARE_NODE_FIELD(relation);
 	COMPARE_NODE_FIELD(cols);
 	COMPARE_NODE_FIELD(selectStmt);
@@ -896,6 +901,7 @@ _equalInsertStmt(InsertStmt *a, InsertStmt *b)
 static bool
 _equalDeleteStmt(DeleteStmt *a, DeleteStmt *b)
 {
+	COMPARE_SCALAR_FIELD(isMergeAction);
 	COMPARE_NODE_FIELD(relation);
 	COMPARE_NODE_FIELD(usingClause);
 	COMPARE_NODE_FIELD(whereClause);
@@ -907,6 +913,7 @@ _equalDeleteStmt(DeleteStmt *a, DeleteStmt *b)
 static bool
 _equalUpdateStmt(UpdateStmt *a, UpdateStmt *b)
 {
+	COMPARE_SCALAR_FIELD(isMergeAction);
 	COMPARE_NODE_FIELD(relation);
 	COMPARE_NODE_FIELD(targetList);
 	COMPARE_NODE_FIELD(whereClause);
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index d0ba12c..65b5347 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -332,6 +332,7 @@ _outModifyTable(StringInfo str, ModifyTable *node)
 	WRITE_NODE_FIELD(returningLists);
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_INT_FIELD(epqParam);
+	WRITE_NODE_FIELD(mergeActPlan);
 }
 
 static void
@@ -2022,6 +2023,53 @@ _outQuery(StringInfo str, Query *node)
 	WRITE_NODE_FIELD(rowMarks);
 	WRITE_NODE_FIELD(setOperations);
 	WRITE_NODE_FIELD(constraintDeps);
+	WRITE_BOOL_FIELD(isMergeAction);
+	WRITE_BOOL_FIELD(matched);
+	WRITE_INT_FIELD(sourceAttrNo);
+	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)
+{
+	WRITE_NODE_TYPE("MERGEACTION");
+
+	_outPlanInfo(str, (Plan *)node);
+
+	WRITE_ENUM_FIELD(operation, CmdType);
+	WRITE_BOOL_FIELD(matched);
+	WRITE_NODE_FIELD(flattenedqual);
+	WRITE_NODE_FIELD(flattenedtlist);
+}
+
+static void
+_outMergeActionSet(StringInfo str, MergeActionSet *node)
+{
+	WRITE_NODE_TYPE("MERGEACTIONSET");
+
+	WRITE_INT_FIELD(result_relation);
+	WRITE_NODE_FIELD(actions);
 }
 
 static void
@@ -2907,6 +2955,18 @@ _outNode(StringInfo str, void *obj)
 			case T_XmlSerialize:
 				_outXmlSerialize(str, obj);
 				break;
+			case T_MergeAction:
+				_outMergeAction(str, obj);
+				break;
+			case T_MergeActionSet:
+				_outMergeActionSet(str, obj);
+				break;
+			case T_MergeStmt:
+				_outMergeStmt(str, obj);
+				break;
+			case T_MergeConditionAction:
+				_outMergeConditionAction(str,obj);
+				break;			
 
 			default:
 
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 0a2edcb..0aeab17 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -219,6 +219,10 @@ _readQuery(void)
 	READ_NODE_FIELD(rowMarks);
 	READ_NODE_FIELD(setOperations);
 	READ_NODE_FIELD(constraintDeps);
+	READ_BOOL_FIELD(isMergeAction);
+	READ_BOOL_FIELD(matched);
+	READ_INT_FIELD(sourceAttrNo);
+	READ_NODE_FIELD(mergeActQry);
 
 	READ_DONE();
 }
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 2115cc0..f5df243 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -3919,7 +3919,7 @@ make_result(PlannerInfo *root,
 ModifyTable *
 make_modifytable(CmdType operation, List *resultRelations,
 				 List *subplans, List *returningLists,
-				 List *rowMarks, int epqParam)
+				 List *rowMarks, List *mergeActPlans, int epqParam)
 {
 	ModifyTable *node = makeNode(ModifyTable);
 	Plan	   *plan = &node->plan;
@@ -3972,6 +3972,8 @@ make_modifytable(CmdType operation, List *resultRelations,
 	node->returningLists = returningLists;
 	node->rowMarks = rowMarks;
 	node->epqParam = epqParam;
+	if (operation == CMD_MERGE)
+		node->mergeActPlan = mergeActPlans;
 
 	return node;
 }
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 3950ab4..c627e6e 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -102,7 +102,8 @@ static void get_column_info_for_window(PlannerInfo *root, WindowClause *wc,
 						   int *ordNumCols,
 						   AttrNumber **ordColIdx,
 						   Oid **ordOperators);
-
+static ModifyTable *merge_action_planner(PlannerInfo *root, Plan *mainPlan);
+static MergeActionSet *merge_action_set_planner(PlannerInfo *root, Plan *mainPlan);
 
 /*****************************************************************************
  *
@@ -452,6 +453,27 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	}
 
 	/*
+	* for MERGE command, we need to preprocess 
+	* the expressions for merge actions too.
+	*/
+	if(parse->commandType == CMD_MERGE)
+	{
+		ListCell *e;
+
+		foreach(e, parse->mergeActQry)
+		{
+			Query *actqry = (Query *)lfirst(e);
+			
+			actqry->targetList = (List *) preprocess_expression(root, 
+										(Node *) actqry->targetList,
+										EXPRKIND_TARGET);
+			actqry->jointree->quals = preprocess_expression(root, 
+										(Node *) actqry->jointree->quals,
+										EXPRKIND_QUAL);
+		}
+	}
+
+	/*
 	 * In some cases we may want to transfer a HAVING clause into WHERE. We
 	 * cannot do so if the HAVING clause contains aggregates (obviously) or
 	 * volatile functions (since a HAVING clause is supposed to be executed
@@ -528,6 +550,7 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 		{
 			List	   *returningLists;
 			List	   *rowMarks;
+			List 		*mergeAction;
 
 			/*
 			 * Deal with the RETURNING clause if any.  It's convenient to pass
@@ -559,12 +582,19 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 			else
 				rowMarks = root->rowMarks;
 
+			/*if here is a MERGE command, we need to plan the actions too*/
+			if(parse->commandType == CMD_MERGE)
+				mergeAction = list_make1(merge_action_set_planner(root, plan));
+			else
+				mergeAction = NIL;
+			
 			plan = (Plan *) make_modifytable(parse->commandType,
 										   copyObject(root->resultRelations),
 											 list_make1(plan),
 											 returningLists,
 											 rowMarks,
-											 SS_assign_special_param(root));
+											 mergeAction,
+											 SS_assign_special_param(root));			
 		}
 	}
 
@@ -585,6 +615,130 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 }
 
 /*
+to generate the merge action set for the main plan. 
+Call this function after the grouping_planner()
+
+Only works for MERGE command
+*/
+static MergeActionSet *
+merge_action_set_planner(PlannerInfo *root, Plan *mainPlan)
+{
+	MergeActionSet *result;
+	Query *mainQry = root->parse;
+	ListCell *l;
+	PlannerInfo subroot;
+
+	/*for non-merge command, no need to plan the merge actions*/
+	if(mainQry->commandType != CMD_MERGE ||
+		mainQry->mergeActQry == NIL)
+		return NULL;
+
+	/*do a copy of the root info*/
+	memcpy(&subroot, root, sizeof(PlannerInfo));
+
+	/*create the result node*/
+	result = makeNode(MergeActionSet);
+	result->result_relation = mainQry->resultRelation;
+	result->actions = NIL;
+
+	/*plan the actions one by one*/	
+	foreach(l, mainQry->mergeActQry)
+	{
+		ModifyTable *actplan;
+
+		/*put the action query into the subroot*/
+		subroot.parse = (Query *) lfirst(l);
+		actplan = merge_action_planner(&subroot, mainPlan);
+		result->actions = lappend(result->actions, actplan);
+	}
+	return result;
+}
+
+/* create plan for a single merge action */
+static ModifyTable *
+merge_action_planner(PlannerInfo *root, Plan *mainPlan)
+{
+	Query *parse = root->parse;
+	MergeAction	*actplan;
+	ModifyTable *result;
+
+	List	   	*returningLists;
+	List 		*rowMarks;
+
+	/*
+	 * no having clause in a merge action
+	 */
+	Assert(parse->havingQual == NULL);
+
+	/*
+	 * Create the action plan node
+	 */
+	actplan = makeNode(MergeAction);
+	actplan->operation = parse->commandType;
+	actplan->matched = parse->matched;
+
+	/* copy the cost from the top_plan */
+	actplan->plan.startup_cost = mainPlan->startup_cost;
+	actplan->plan.total_cost = mainPlan->total_cost;
+	actplan->plan.plan_rows = mainPlan->plan_rows;
+	actplan->plan.plan_width = mainPlan->plan_width;
+
+	/*
+	* Here, the quals expressions are flattened, which is accepted
+	* by deparse functions in EXPLAIN.
+	* But, these expressions will be processed by push_up_vars
+	* latterly and become not flat again. 
+	* So, we need to keep a copy of current quals for explaining.  
+	*/
+	actplan->flattenedqual = (List *) copyObject(parse->jointree->quals);
+	actplan->plan.qual = (List *)parse->jointree->quals;
+
+	/* prepare the target list */
+	if (parse->targetList)
+	{
+		actplan->plan.targetlist = preprocess_targetlist(root,
+										parse->targetList);
+		/*the target list should also be copied for EXPLAIN*/
+		actplan->flattenedtlist = (List *) copyObject(actplan->plan.targetlist);		
+	}
+
+	/*
+	*In general situation, all the vars in target list and quals are flattened.
+	*But, we want them to point to the attributes of the top join plan, not to
+	*the subplans. So push them up again here. 
+	*/
+	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,
+							  list_make1_int(parse->resultRelation),
+							  list_make1(actplan),
+							  returningLists,
+							  rowMarks,
+							  NIL,
+							  SS_assign_special_param(root));
+	return result;
+}
+
+/*
  * preprocess_expression
  *		Do subquery_planner's preprocessing work for an expression,
  *		which can be a targetlist, a WHERE clause (including JOIN/ON
@@ -729,6 +883,7 @@ inheritance_planner(PlannerInfo *root)
 	List	   *returningLists = NIL;
 	List	   *rtable = NIL;
 	List	   *rowMarks;
+	List	   *mergeActSets = NIL;
 	List	   *tlist;
 	PlannerInfo subroot;
 	ListCell   *l;
@@ -790,6 +945,66 @@ inheritance_planner(PlannerInfo *root)
 													appinfo->child_relid);
 			returningLists = lappend(returningLists, rlist);
 		}
+
+		/*
+		*For a merge command, we need to generate a set of action plans corresponding
+		*to current result relations. 
+		*The adjust_appendrel_attrs() will not process the merge action list of 
+		*the main query. And, We need to do this here for a MERGE command. 
+		*In fact, no need to do a full query tree mutator on the action queries. 
+		*only adjust the target list and quals.
+		*/
+		if (parse->commandType == CMD_MERGE)
+		{
+			ListCell *e;
+			MergeActionSet *maset;
+
+			/*
+			*the parse in subroot now is a copy of the main query of current result relation
+			*Here we need to generate a copy of the action queries and shift their target table
+			*to current result relation
+			*/
+			subroot.parse->mergeActQry = NIL;
+			
+			foreach(e, parse->mergeActQry)
+			{
+				Query *actqry = (Query *)lfirst(e);
+				Query *newactqry = makeNode(Query);
+
+				/*copy most of the common fields from original query*/
+				*newactqry = *actqry;
+				
+				/*reset the result relation to current child table*/
+				newactqry->resultRelation = subroot.parse->resultRelation;
+
+				/*make the range table to be consistent with current main query*/
+				newactqry->rtable = subroot.parse->rtable;
+
+				/*adjust the target list*/	
+				newactqry->targetList = (List *) adjust_appendrel_attrs(
+															(Node *) actqry->targetList,
+															appinfo);
+				newactqry->targetList = adjust_inherited_tlist(newactqry->targetList, 
+															appinfo);
+				/*and qual*/
+				newactqry->jointree = makeNode(FromExpr);
+				newactqry->jointree->fromlist = subroot.parse->jointree->fromlist;
+				newactqry->jointree->quals = adjust_appendrel_attrs(
+															actqry->jointree->quals,
+															appinfo);
+
+				/*put this new action query in to the action list of current main query*/
+				subroot.parse->mergeActQry = lappend(subroot.parse->mergeActQry, newactqry);				
+			}
+
+			/*
+			* now we have a complete query (main query + action queries) that has been 
+			*shifted to  current result relation. Plan these actions here.
+			*/
+			maset = merge_action_set_planner(&subroot, subplan);
+			Assert(maset != NULL);
+			mergeActSets = lappend(mergeActSets, maset);
+		}
 	}
 
 	root->resultRelations = resultRelations;
@@ -842,6 +1057,7 @@ inheritance_planner(PlannerInfo *root)
 									 subplans,
 									 returningLists,
 									 rowMarks,
+									 mergeActSets,
 									 SS_assign_special_param(root));
 }
 
diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
index 59d3518..6faa234 100644
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -78,25 +78,64 @@ preprocess_targetlist(PlannerInfo *root, List *tlist)
 								  result_relation, range_table);
 
 	/*
-	 * for "update" and "delete" queries, add ctid of the result relation into
+	for MERGE command, we also need to expend the target list of the main query.
+	Note that, the target list of main query is the combination of attrs
+	from Source table and target table. We only want to expend the part
+	of target table. 
+
+	We do this in an aggressive way:
+	1. Truncate the old target list, keep only the entries for source table
+	2. expend the target list of result relation from an NIL list. 
+	3. Append this new list at the end of old target list. 
+	*/
+	if (command_type == CMD_MERGE)
+	{
+		ListCell *l;
+		List *TLforResultRelatoin = NIL;
+		int new_resno;
+		
+		Assert(parse->sourceAttrNo > 0);
+		
+		tlist = list_truncate(tlist, parse->sourceAttrNo);
+		
+		TLforResultRelatoin =  expand_targetlist(TLforResultRelatoin, command_type,  
+													result_relation, range_table);
+		new_resno = parse->sourceAttrNo + 1;
+		foreach(l, TLforResultRelatoin)
+		{
+			TargetEntry *te = (TargetEntry *)lfirst(l);
+			te->resno = new_resno++;
+		}
+
+		tlist = list_concat(tlist, TLforResultRelatoin);		
+	}
+
+	/*
+	 * 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 expand 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;
 
 		var = makeVar(result_relation, SelfItemPointerAttributeNumber,
 					  TIDOID, -1, 0);
-
 		tle = makeTargetEntry((Expr *) var,
 							  list_length(tlist) + 1,
 							  pstrdup("ctid"),
 							  true);
-
 		/*
 		 * For an UPDATE, expand_targetlist already created a fresh tlist. For
 		 * DELETE, better do a listCopy so that we don't destructively modify
@@ -339,6 +378,7 @@ expand_targetlist(List *tlist, int command_type,
 					}
 					break;
 				case CMD_UPDATE:
+				case CMD_MERGE:
 					if (!att_tup->attisdropped)
 					{
 						new_expr = (Node *) makeVar(result_relation,
diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index 68fe92f..1690a1f 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -101,9 +101,6 @@ static Bitmapset *translate_col_privs(const Bitmapset *parent_privs,
 static Node *adjust_appendrel_attrs_mutator(Node *node,
 							   AppendRelInfo *context);
 static Relids adjust_relid_set(Relids relids, Index oldrelid, Index newrelid);
-static List *adjust_inherited_tlist(List *tlist,
-					   AppendRelInfo *context);
-
 
 /*
  * plan_set_operations
@@ -1740,8 +1737,9 @@ adjust_relid_set(Relids relids, Index oldrelid, Index newrelid)
  * scribble on.
  *
  * Note that this is not needed for INSERT because INSERT isn't inheritable.
+ * But the INSERT actions in MERGE need this function
  */
-static List *
+List *
 adjust_inherited_tlist(List *tlist, AppendRelInfo *context)
 {
 	bool		changed_it = false;
diff --git a/src/backend/optimizer/util/var.c b/src/backend/optimizer/util/var.c
index 92c2208..0059c3c 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 +689,79 @@ 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:
+ *	1. the source table, which may be a subquery or a plain table
+ *	2. the entry of the target table, which is a plain table
+ *	3. join expression with the source 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 opposite 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;
+
+	context.varno_source = Merge_SourceTableRTindex;
+	context.varno_target = actqry->resultRelation;
+	context.varno_join = Merge_TopJoinTableRTindex;
+	context.offset_source = 0;	
+	context.offset_target = actqry->sourceAttrNo;
+
+	push_up_merge_action_vars_walker((Node *)actplan->plan.targetlist, 
+											&context);
+	push_up_merge_action_vars_walker((Node *)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 target 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 a1320f5..d94446e 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);
@@ -175,6 +176,10 @@ transformStmt(ParseState *pstate, Node *parseTree)
 			result = transformUpdateStmt(pstate, (UpdateStmt *) parseTree);
 			break;
 
+		case T_MergeStmt:
+			result = transformMergeStmt(pstate, (MergeStmt *)parseTree);
+			break;
+
 		case T_SelectStmt:
 			{
 				SelectStmt *n = (SelectStmt *) parseTree;
@@ -245,6 +250,7 @@ analyze_requires_snapshot(Node *parseTree)
 		case T_DeleteStmt:
 		case T_UpdateStmt:
 		case T_SelectStmt:
+		case T_MergeStmt:
 			result = true;
 			break;
 
@@ -282,21 +288,27 @@ 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.
+	 * The input stmt could be a MergeDelete node.
+	 * In this case, we don't need the process on range table.
 	 */
-	transformFromClause(pstate, stmt->usingClause);
+	if (!stmt->isMergeAction)
+	{
+		/* 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");
 
@@ -347,6 +359,8 @@ 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 statement is always a VALUES clause*/
 	isGeneralSelect = (selectStmt && selectStmt->valuesLists == NIL);
 
 	/*
@@ -382,7 +396,8 @@ 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 (!stmt->isMergeAction) /* 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 */
@@ -1726,16 +1741,18 @@ 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 (!stmt->isMergeAction) /* 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);
 
@@ -2237,3 +2254,329 @@ applyLockingClause(Query *qry, Index rtindex,
 	rc->pushedDown = pushedDown;
 	qry->rowMarks = lappend(qry->rowMarks, rc);
 }
+
+/*
+ * transform an 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;
+
+	/*
+	 * First, we need to make sure that DELETE and UPDATE
+	 * actions are only taken in MATCHED condition,
+	 * and INSERTs are only taken when not MATCHED
+	 */
+	switch(condact->action->type)
+	{
+		case T_DeleteStmt:/*a delete action*/
+			{
+				DeleteStmt *deleteact = (DeleteStmt *) condact->action;
+				Assert(deleteact->isMergeAction);
+
+				if (!condact->match)
+					ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						errmsg("The DELETE action in MERGE command is not allowed when NOT MATCHED")));
+
+				/*put new right code to the result relation.
+				This line chages the RTE in range table directly*/
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_DELETE;
+
+				deleteact->relation = stmt->relation;
+				deleteact->usingClause = list_make1(stmt->source);
+				deleteact->whereClause = condact->condition;
+
+				/*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");
+
+				actqry->isMergeAction = true;
+				actqry->matched = condact->match;
+
+				return actqry;
+			}
+			break;
+		case T_UpdateStmt:/*an update action*/
+			{
+				UpdateStmt *updateact = (UpdateStmt *) condact->action;
+				Assert(updateact->isMergeAction);
+
+				if (!condact->match)
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							errmsg("The UPDATE action in MERGE command is not allowed when NOT MATCHED")));
+
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_UPDATE;
+
+				/*the "targetlist" of the updateact is filled in the parser */
+				updateact->relation = stmt->relation;
+				updateact->fromClause = list_make1(stmt->source);
+				updateact->whereClause = condact->condition;
+
+				/*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");
+
+				actqry->isMergeAction = true;
+				actqry->matched = condact->match;
+
+				return actqry;
+			}
+			break;
+		case T_InsertStmt:/*an insert action*/
+			{
+				InsertStmt *insertact = (InsertStmt *) condact->action;
+				Assert(insertact->isMergeAction);
+
+				if(condact->match)
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+							errmsg("The INSERT action in MERGE command is not allowed when MATCHED")));
+
+				pstate->p_target_rangetblentry->requiredPerms |= ACL_INSERT;
+
+				/*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 target 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 consistency 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*/
+				actqry->jointree = makeFromExpr(pstate->p_joinlist,
+											transformWhereClause(pstate,
+															condact->condition,
+															"WHERE"));
+				if(!IsA(actqry, Query) ||
+					actqry->commandType != CMD_INSERT||
+					actqry->utilityStmt != NULL)
+					elog(ERROR, "improper INSERT action in merge stmt");
+
+				actqry->isMergeAction = true;
+				actqry->matched = condact->match;
+
+				return actqry;
+			}
+			break;
+		case T_MergeDoNothing:
+			{
+				MergeDoNothing *nothingact;
+
+				nothingact = (MergeDoNothing *)(condact->action);
+
+				Assert(IsA(nothingact,MergeDoNothing));
+
+				actqry = makeNode(Query);
+
+				actqry->jointree = makeFromExpr(pstate->p_joinlist,
+											transformWhereClause(pstate,
+															condact->condition,
+															"WHERE"));
+				actqry->rtable = pstate->p_rtable;
+
+				actqry->commandType = CMD_DONOTHING;
+				actqry->isMergeAction = true;
+				actqry->matched = condact->match;
+
+				return actqry;
+			}
+			break;	
+		default:
+			elog(ERROR, "unknown MERGE action type %d", condact->action->type);
+			break;
+	}
+
+	/*never comes here*/
+	return NULL;
+}
+
+static Query *
+transformMergeStmt(ParseState *pstate, MergeStmt *stmt)
+{
+	Query	   *qry;
+
+	ColumnRef *starRef;
+	ResTarget *starResTarget;
+	ListCell *act;
+	ListCell *l;
+	JoinExpr *joinexp;
+	RangeTblEntry *resultRTE = NULL;
+	RangeTblEntry *topjoinRTE = NULL;
+	RangeTblEntry *sourceRTE = NULL;
+	
+	/*firstly, create the output node structure*/
+	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 target 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 transforming the FROM clause, acquire write lock on the
+	 * target relation. We don't want to add it to the range table yet,
+	 * so we use setTargetTableLock() instead of setTargetTable().
+	 */
+	setTargetTableLock(pstate, stmt->relation);
+
+	/* 
+	* Make the join expression on source table and target table, 
+	* as the only element in FROM list
+	*/
+	joinexp = makeNode(JoinExpr);
+	joinexp->jointype = JOIN_LEFT;
+	joinexp->isNatural = FALSE;
+	joinexp->larg = stmt->source;
+	joinexp->rarg = (Node *)stmt->relation;
+	joinexp->quals = stmt->matchCondition;
+
+	/*
+	 * transform the FROM clause. The target relation and
+	 * source relation will be added to the range table 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 a WHERE clause here. Set it null. */
+	qry->jointree = makeFromExpr(pstate->p_joinlist, NULL);
+
+	/*
+	*The range table of a MERGE command query has only 3 RTE.
+	*RTE 1 is the source table, RTE 2 is the target table, RTE 3 is the left join
+	*between source and target table. 
+	*/
+	qry->rtable = pstate->p_rtable;
+
+	/*Set RTE 2 as the result relation of query*/
+	qry->resultRelation = 2;
+	resultRTE = rt_fetch(qry->resultRelation, pstate->p_rtable);
+	if(resultRTE->relid != pstate->p_target_relation->rd_id)
+		elog(ERROR, "The target relation entry should be the second one in range table");
+
+	resultRTE->requiredPerms = ACL_SELECT;
+	resultRTE->inh = interpretInhOption(stmt->relation->inhOpt);
+	pstate->p_target_rangetblentry = resultRTE;
+
+	/*
+	  *we also need to find out how many attributes are there in the source table. 
+	  *There are many ways to do this. Here, I choose to scan the join var list of the
+	  *top join table entry. And count how many vars belong to source table.
+	  */
+	topjoinRTE = rt_fetch(Merge_TopJoinTableRTindex, pstate->p_rtable);
+	Assert(topjoinRTE->jointype == JOIN_LEFT);
+	
+	qry->sourceAttrNo = 0;
+	foreach(l, topjoinRTE->joinaliasvars)
+	{
+		Var *jv = (Var *)lfirst(l);
+
+		if(jv->varno == Merge_SourceTableRTindex)
+			qry->sourceAttrNo++;
+	}
+	/*lets do a simple check here*/
+	sourceRTE = rt_fetch(Merge_SourceTableRTindex, pstate->p_rtable);
+	Assert(qry->sourceAttrNo == list_length(sourceRTE->eref->colnames));
+
+	/*
+	 * For each action, transform it to a separate query.
+	 * The action queries share the range table with the main query.
+	 *
+	 * In other words, in the extra conditions of the sub actions,
+	 * we don't allow involvement of new tables
+	 */
+	qry->mergeActQry = NIL;
+
+	foreach(act,stmt->actions)
+	{
+		MergeConditionAction *mca = (MergeConditionAction *) lfirst(act);
+		Query *actqry;
+
+		/* transform the act (and its condition) as a single 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;
+
+		/*record the source attr number in each action query, for latter use*/
+		actqry->sourceAttrNo = qry->sourceAttrNo;
+
+		/* put it into the list */
+		qry->mergeActQry = lappend(qry->mergeActQry, actqry);
+	}
+
+	/*
+	* set the sublink mark at the last.
+	* Thus, the sublink in actions will be counted in.
+	*/	
+	qry->hasSubLinks = pstate->p_hasSubLinks;
+ 
+	return qry;
+}
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index b38b2b1..fb792d3 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -211,6 +211,11 @@ static TypeName *TableFuncTypeName(List *columns);
 		DeallocateStmt PrepareStmt ExecuteStmt
 		DropOwnedStmt ReassignOwnedStmt
 		AlterTSConfigurationStmt AlterTSDictionaryStmt
+		MergeStmt
+
+%type <node>	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
@@ -480,7 +485,7 @@ static TypeName *TableFuncTypeName(List *columns);
 	DEFERRABLE DEFERRED DEFINER DELETE_P DELIMITER DELIMITERS DESC
 	DICTIONARY DISABLE_P DISCARD DISTINCT DO DOCUMENT_P DOMAIN_P DOUBLE_P DROP
 
-	EACH ELSE ENABLE_P ENCODING ENCRYPTED END_P ENUM_P ESCAPE EXCEPT
+	EACH ELSE ENABLE_P ENCODING ENCRYPTED END_P ENUM_P ERROR_P ESCAPE EXCEPT
 	EXCLUDE EXCLUDING EXCLUSIVE EXECUTE EXISTS EXPLAIN EXTERNAL EXTRACT
 
 	FALSE_P FAMILY FETCH FIRST_P FLOAT_P FOLLOWING FOR FORCE FOREIGN FORWARD
@@ -503,7 +508,7 @@ static TypeName *TableFuncTypeName(List *columns);
 	LEAST LEFT LEVEL LIKE LIMIT LISTEN LOAD LOCAL LOCALTIME LOCALTIMESTAMP
 	LOCATION LOCK_P LOGIN_P
 
-	MAPPING MATCH MAXVALUE MINUTE_P MINVALUE MODE MONTH_P MOVE
+	MAPPING MATCH MATCHED MAXVALUE MERGE MINUTE_P MINVALUE MODE MONTH_P MOVE
 
 	NAME_P NAMES NATIONAL NATURAL NCHAR NEXT NO NOCREATEDB
 	NOCREATEROLE NOCREATEUSER NOINHERIT NOLOGIN_P NONE NOSUPERUSER
@@ -518,7 +523,7 @@ static TypeName *TableFuncTypeName(List *columns);
 
 	QUOTE
 
-	RANGE READ REAL REASSIGN RECHECK RECURSIVE REF REFERENCES REINDEX
+	RAISE RANGE READ REAL REASSIGN RECHECK RECURSIVE REF REFERENCES REINDEX
 	RELATIVE_P RELEASE RENAME REPEATABLE REPLACE REPLICA RESET RESTART
 	RESTRICT RETURNING RETURNS REVOKE RIGHT ROLE ROLLBACK ROW ROWS RULE
 
@@ -726,6 +731,7 @@ stmt :
 			| ListenStmt
 			| LoadStmt
 			| LockStmt
+			| MergeStmt
 			| NotifyStmt
 			| PrepareStmt
 			| ReassignOwnedStmt
@@ -6988,6 +6994,7 @@ ExplainableStmt:
 			| InsertStmt
 			| UpdateStmt
 			| DeleteStmt
+			| MergeStmt
 			| DeclareCursorStmt
 			| CreateAsStmt
 			| ExecuteStmt					/* by default all are $$=$1 */
@@ -7333,6 +7340,112 @@ set_target_list:
 /*****************************************************************************
  *
  *		QUERY:
+ *				MERGE STATEMENT
+ *
+ *****************************************************************************/
+
+
+MergeStmt:
+			MERGE INTO relation_expr_opt_alias
+			USING  table_ref
+			ON a_expr
+			merge_condition_action_list
+				{
+					MergeStmt *m = makeNode(MergeStmt);
+
+					m->relation = $3;
+					m->source = $5;
+					m->matchCondition = $7;
+					m->actions = $8;
+
+					$$ = (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*/	{ $$ = true; }
+				;
+
+merge_action:
+			DELETE_P
+				{
+					DeleteStmt *n = makeNode(DeleteStmt);
+					n->isMergeAction = true;
+					$$ = (Node *) n;
+				}
+			| UPDATE SET set_clause_list
+				{
+					UpdateStmt *n = makeNode(UpdateStmt);
+					n->targetList = $3;
+					n->isMergeAction = true;
+					
+					$$ = (Node *) n;
+				}
+			| INSERT values_clause
+				{
+					InsertStmt *n = makeNode(InsertStmt);
+					n->cols = NIL;
+					n->selectStmt = $2;
+					n->isMergeAction = true;
+					
+					$$ = (Node *) n;
+				}
+
+			| INSERT '(' insert_column_list ')' values_clause
+				{
+					InsertStmt *n = makeNode(InsertStmt);
+					n->cols = $3;
+					n->selectStmt = $5;
+					n->isMergeAction = true;
+					
+					$$ = (Node *) n;
+				}
+			| INSERT DEFAULT VALUES
+				{
+					InsertStmt *n = makeNode(InsertStmt);
+					n->cols = NIL;
+					n->selectStmt = NULL;
+					n->isMergeAction = true;
+					
+					$$ = (Node *) n;
+				}
+			| DO NOTHING
+				{
+					$$ = (Node *) makeNode(MergeDoNothing);
+				}
+			;
+
+
+
+/*****************************************************************************
+ *
+ *		QUERY:
  *				CURSOR STATEMENTS
  *
  *****************************************************************************/
@@ -10954,6 +11067,7 @@ unreserved_keyword:
 			| ENCODING
 			| ENCRYPTED
 			| ENUM_P
+			| ERROR_P
 			| ESCAPE
 			| EXCLUDE
 			| EXCLUDING
@@ -11007,7 +11121,9 @@ unreserved_keyword:
 			| LOGIN_P
 			| MAPPING
 			| MATCH
+			| MATCHED
 			| MAXVALUE
+			| MERGE
 			| MINUTE_P
 			| MINVALUE
 			| MODE
@@ -11050,6 +11166,7 @@ unreserved_keyword:
 			| PROCEDURAL
 			| PROCEDURE
 			| QUOTE
+			| RAISE
 			| RANGE
 			| READ
 			| REASSIGN
diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index 16ca583..c3e8038 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -214,6 +214,25 @@ 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..63f963a 100644
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -1836,6 +1836,41 @@ RewriteQuery(Query *parsetree, List *rewrite_events)
 	return rewritten;
 }
 
+/*if the merge action type has already been processed by rewriter*/
+#define insert_rewrite (1<<0)
+#define delete_rewrite (1<<1)
+#define update_rewrite (1<<2)
+
+/*if the merge action type is fully replace by rules.*/
+#define	insert_instead (1<<3)
+#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 -
@@ -1861,7 +1896,148 @@ 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, we have a set of action queries (not subquery).
+		 * each of these action queries should rewritten with RewriteQuery().
+		 */
+		ListCell   *l;
+		int 	flag = 0;
+		List 	*pre_qry = NIL;
+		List 	*post_qry = NIL;
+
+		querylist = NIL;
+
+		/*rewrite the merge action queries one by one.*/
+		foreach(l, parsetree->mergeActQry)
+		{
+			List *queryList4action = NIL;
+			Query *actionqry;
+			Query *q;
+
+			actionqry = lfirst(l);
+
+			/* no rewriting for DO NOTHING action*/
+			if (actionqry->commandType == CMD_DONOTHING)
+				continue;
+
+			/*
+			 * if this kind of actions are fully replaced by rules,
+			 * we change it into a DO NOTHING action
+			 */
+			if (merge_action_instead(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);
+				actionqry->commandType = CMD_DONOTHING;
+				actionqry->targetList = NIL;
+				continue;
+			}
+
+			/* if this kind of actions are already processed by rewriter, skip it.*/
+			if (merge_action_already_rewrite(actionqry->commandType, flag))
+			{
+				RewriteQuery(actionqry, NIL);
+				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 the flag */
+			set_action_rewrite(actionqry->commandType, flag);
+
+			/*
+			 * if the returning list is empty, 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);
+				actionqry->commandType = CMD_DONOTHING;
+				actionqry->targetList = NIL;
+				continue;
+			}
+
+			/*
+			 * if the rewriter return a non-NIL list, the merge action query
+			 * could be one element in it.
+			 * if so, it must be the head (for INSERT action)
+			 * or tail (for UPDATE/DELETE action).
+			 */
+
+			/* test the list head */
+			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);
+
+				continue;
+			}
+
+			/*test the list tail*/
+			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);
+				continue;
+			}
+
+			/*
+			 * here, the merge action query is not in the rewritten query list,
+			 * which means the action is replaced by INSTEAD rule(s).
+			 * We need to change it into do noting 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);
+			actionqry->commandType = CMD_DONOTHING;
+			actionqry->targetList = NIL;
+		}
+
+		/*
+		 * 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/postgres.c b/src/backend/tcop/postgres.c
index 48b77d8..12628a4 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -979,7 +979,7 @@ exec_simple_query(const char *query_string)
 												NULL, 0);
 
 		plantree_list = pg_plan_queries(querytree_list, 0, NULL);
-
+//printf("the plann is \n%s\n", nodeToString(plantree_list));
 		/* Done with the snapshot used for parsing/planning */
 		if (snapshot_set)
 			PopActiveSnapshot();
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 44cc401..3ac1ab0 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",
@@ -1406,6 +1407,10 @@ CreateCommandTag(Node *parsetree)
 			tag = "SELECT";
 			break;
 
+		case T_MergeStmt:
+			tag = "MERGE";
+			break;
+
 			/* utility statements --- same whether raw or cooked */
 		case T_TransactionStmt:
 			{
@@ -2243,6 +2248,7 @@ GetCommandLogLevel(Node *parsetree)
 		case T_InsertStmt:
 		case T_DeleteStmt:
 		case T_UpdateStmt:
+		case T_MergeStmt:
 			lev = LOGSTMT_MOD;
 			break;
 
diff --git a/src/include/commands/trigger.h b/src/include/commands/trigger.h
index 267a08e..51d0f11 100644
--- a/src/include/commands/trigger.h
+++ b/src/include/commands/trigger.h
@@ -164,6 +164,8 @@ extern void ExecBSTruncateTriggers(EState *estate,
 					   ResultRelInfo *relinfo);
 extern void ExecASTruncateTriggers(EState *estate,
 					   ResultRelInfo *relinfo);
+extern void ExecBSMergeTriggers(ModifyTableState *mt_state);
+extern void ExecASMergeTriggers(ModifyTableState *mt_state);
 
 extern void AfterTriggerBeginXact(void);
 extern void AfterTriggerBeginQuery(void);
diff --git a/src/include/executor/nodeModifyTable.h b/src/include/executor/nodeModifyTable.h
index 67ba3e8..422e3ce 100644
--- a/src/include/executor/nodeModifyTable.h
+++ b/src/include/executor/nodeModifyTable.h
@@ -16,6 +16,7 @@
 #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..d55375c 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1032,9 +1032,23 @@ 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? */
+	MergeActionSet **mt_mergeActPstates; /*the list of the planstate of merge command actions. 
+											NULL if this is not a merge command.
+											The elements if it are still MergeActionSet nodes. 
+											But the action list in these nodes are ModifyTableState */
 } 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..5bb5706 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -44,6 +44,8 @@ typedef enum NodeTag
 	T_Plan = 100,
 	T_Result,
 	T_ModifyTable,
+	T_MergeAction,
+	T_MergeActionSet,
 	T_Append,
 	T_RecursiveUnion,
 	T_BitmapAnd,
@@ -86,6 +88,7 @@ typedef enum NodeTag
 	T_PlanState = 200,
 	T_ResultState,
 	T_ModifyTableState,
+	T_MergeActionState,
 	T_AppendState,
 	T_RecursiveUnionState,
 	T_BitmapAndState,
@@ -347,6 +350,10 @@ typedef enum NodeTag
 	T_AlterUserMappingStmt,
 	T_DropUserMappingStmt,
 	T_AlterTableSpaceOptionsStmt,
+	T_MergeStmt,
+	T_MergeConditionAction,
+	T_MergeDoNothing,
+	T_MergeError,
 
 	/*
 	 * TAGS FOR PARSE TREE NODES (parsenodes.h)
@@ -511,6 +518,8 @@ typedef enum CmdType
 	CMD_UPDATE,					/* update stmt */
 	CMD_INSERT,					/* insert stmt */
 	CMD_DELETE,
+	CMD_MERGE,					/* merge stmt */
+	CMD_DONOTHING,				/*DO NOTHING action in MERGE command*/
 	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 e896dc7..696036d 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -149,8 +149,24 @@ typedef struct Query
 
 	List	   *constraintDeps;	/* a list of pg_constraint OIDs that the query
 								 * depends on to be semantically valid */
+
+	/* fields for MERGE command */
+	bool	isMergeAction;		/* if this query is a merge action. */
+	bool	matched;			/* this is a MATCHED action or NOT */
+	int		sourceAttrNo; /*the number of attributes in source table*/
+	List   *mergeActQry;		/* the list of all the merge actions.
+								 * used only for merge query statement */
 } Query;
 
+/*
+* In MERGE command, the initial MERGE query has only three range table entry
+*The first one is the source table; The second one is the target table; and The
+*third one is the left join entry of them. 
+*During the whole process of a MEREGE command, the rt_index for the source table
+*entry and the join table entry will never change. We set them as constant here. 
+*/
+#define Merge_SourceTableRTindex	1
+#define Merge_TopJoinTableRTindex 	3
 
 /****************************************************************************
  *	Supporting data structures for Parse Trees
@@ -892,6 +908,7 @@ typedef struct CommonTableExpr
 typedef struct InsertStmt
 {
 	NodeTag		type;
+	bool		isMergeAction;	/*if this is a merge insert action*/
 	RangeVar   *relation;		/* relation to insert into */
 	List	   *cols;			/* optional: names of the target columns */
 	Node	   *selectStmt;		/* the source SELECT/VALUES, or NULL */
@@ -905,6 +922,7 @@ typedef struct InsertStmt
 typedef struct DeleteStmt
 {
 	NodeTag		type;
+	bool		isMergeAction;	/*if this is a merge delete action*/
 	RangeVar   *relation;		/* relation to delete from */
 	List	   *usingClause;	/* optional using clause for more tables */
 	Node	   *whereClause;	/* qualifications */
@@ -918,6 +936,7 @@ typedef struct DeleteStmt
 typedef struct UpdateStmt
 {
 	NodeTag		type;
+	bool		isMergeAction;	/*if this is a merge delete action*/
 	RangeVar   *relation;		/* relation to update */
 	List	   *targetList;		/* the target list (of ResTarget) */
 	Node	   *whereClause;	/* qualifications */
@@ -993,6 +1012,54 @@ typedef struct SelectStmt
 	/* Eventually add fields for CORRESPONDING spec here */
 } SelectStmt;
 
+/* ----------------------
+ *		Merge Statement
+ * ----------------------
+ */
+typedef struct MergeStmt
+{
+	NodeTag		type;
+	RangeVar   *relation;		/* target relation for merge */
+
+	/*
+	 * source relations for the merge.
+	 * Currently, we only allow single-source merge,
+	 * so the length of this list should always be 1.
+	 */
+	Node		*source;
+	Node	   	*matchCondition;	/* qualifications of the merge */
+
+	/* list  of MergeConditionAction structure.
+	 * It stores all the matched / not-matched
+	 * conditions and the corresponding actions
+	 * The elements 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;			/* WHEN MATCHED or WHEN NOT MATCHED? */
+	Node	   *condition;		/* the AND condition for this action */
+	Node 	   *action;			/* the actions: delete, insert or update */
+} MergeConditionAction;
+
+typedef struct MergeDoNothing
+{
+	NodeTag 	type;
+} MergeDoNothing;
+
+typedef struct MergeError
+{
+	NodeTag 	type;
+} MergeError;
 
 /* ----------------------
  *		Set Operation node for post-analysis query trees
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 037bc0b..5583f59 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -169,9 +169,38 @@ 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 MergeActionSet nodes. 
+								 * one set for one target relation */
 } ModifyTable;
 
 /* ----------------
+ *	 MergeActionSet node -
+ *		The node contains all actions of MERGE command for one specific target relation 
+ * ----------------
+ */
+typedef struct MergeActionSet
+{
+	NodeTag type;
+	int result_relation;
+	List *actions;
+}MergeActionSet;
+
+/* ----------------
+ *	 MergeAction node -
+ *		The plan node for the actions of MERGE command
+ * ----------------
+ */
+typedef struct MergeAction
+{
+	Plan		plan;
+	CmdType		operation;		/* INSERT, UPDATE, DELETE, DO_NOTHING or RAISE_ERR */
+	bool	 	matched;		/* is this a MATCHED or NOT MATCHED rule? */
+	List	   	*flattenedqual;	/* the flattened qual expression of action */
+	List		*flattenedtlist;/*the fattened target list*/
+} MergeAction;
+
+/* ----------------
  *	 Append node -
  *		Generate the concatenation of the results of sub-plans.
  * ----------------
diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index 35cdd2c..3660e57 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -80,7 +80,7 @@ extern Result *make_result(PlannerInfo *root, List *tlist,
 			Node *resconstantqual, Plan *subplan);
 extern ModifyTable *make_modifytable(CmdType operation, List *resultRelations,
 				 List *subplans, List *returningLists,
-				 List *rowMarks, int epqParam);
+				 List *rowMarks, List *mergeActPlans, int epqParam);
 extern bool is_projection_capable_plan(Plan *plan);
 
 /*
diff --git a/src/include/optimizer/prep.h b/src/include/optimizer/prep.h
index 9df6390..4e8117f 100644
--- a/src/include/optimizer/prep.h
+++ b/src/include/optimizer/prep.h
@@ -52,4 +52,6 @@ extern void expand_inherited_tables(PlannerInfo *root);
 
 extern Node *adjust_appendrel_attrs(Node *node, AppendRelInfo *appinfo);
 
+extern List *adjust_inherited_tlist(List * tlist, AppendRelInfo * context);
+
 #endif   /* PREP_H */
diff --git a/src/include/optimizer/var.h b/src/include/optimizer/var.h
index b0e04a0..ec773f4 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 +33,6 @@ 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 974bb7a..208c3e4 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -141,6 +141,7 @@ PG_KEYWORD("encoding", ENCODING, UNRESERVED_KEYWORD)
 PG_KEYWORD("encrypted", ENCRYPTED, UNRESERVED_KEYWORD)
 PG_KEYWORD("end", END_P, RESERVED_KEYWORD)
 PG_KEYWORD("enum", ENUM_P, UNRESERVED_KEYWORD)
+PG_KEYWORD("error", ERROR_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("escape", ESCAPE, UNRESERVED_KEYWORD)
 PG_KEYWORD("except", EXCEPT, RESERVED_KEYWORD)
 PG_KEYWORD("exclude", EXCLUDE, UNRESERVED_KEYWORD)
@@ -229,7 +230,9 @@ 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)
@@ -296,6 +299,7 @@ PG_KEYWORD("privileges", PRIVILEGES, UNRESERVED_KEYWORD)
 PG_KEYWORD("procedural", PROCEDURAL, UNRESERVED_KEYWORD)
 PG_KEYWORD("procedure", PROCEDURE, UNRESERVED_KEYWORD)
 PG_KEYWORD("quote", QUOTE, UNRESERVED_KEYWORD)
+PG_KEYWORD("raise", RAISE, UNRESERVED_KEYWORD)
 PG_KEYWORD("range", RANGE, UNRESERVED_KEYWORD)
 PG_KEYWORD("read", READ, UNRESERVED_KEYWORD)
 PG_KEYWORD("real", REAL, COL_NAME_KEYWORD)
diff --git a/src/include/parser/parse_clause.h b/src/include/parser/parse_clause.h
index f3d3ee9..b54f530 100644
--- a/src/include/parser/parse_clause.h
+++ b/src/include/parser/parse_clause.h
@@ -19,6 +19,7 @@
 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/expected/merge.out b/src/test/regress/expected/merge.out
new file mode 100644
index 0000000..7ee155a
--- /dev/null
+++ b/src/test/regress/expected/merge.out
@@ -0,0 +1,202 @@
+-- MERGE --
+--  
+-- create basic tables for test, and insert some source rows to work from
+--
+--The Stock table, which records the amount of each item on hand.
+CREATE TABLE Stock(item_id int UNIQUE, balance int);
+NOTICE:  CREATE TABLE / UNIQUE will create implicit index "stock_item_id_key" for table "stock"
+INSERT INTO Stock VALUES (10, 2200);
+INSERT INTO Stock VALUES (20, 1900);
+SELECT * FROM Stock;
+ item_id | balance 
+---------+---------
+      10 |    2200
+      20 |    1900
+(2 rows)
+
+--The Buy table, which records the amount we bought today for each item.
+CREATE TABLE Buy(item_id int, volume int);
+INSERT INTO Buy values(10, 1000);
+INSERT INTO Buy values(30, 300);
+SELECT * FROM Buy;
+ item_id | volume 
+---------+--------
+      10 |   1000
+      30 |    300
+(2 rows)
+
+--The Sale table, which records the amount we sold today for each item.
+CREATE TABLE Sale(item_id int, volume int);
+INSERT INTO Sale VALUES (10, 2200);
+INSERT INTO Sale VALUES (20, 1000);
+SELECT * FROM Sale;
+ item_id | volume 
+---------+--------
+      10 |   2200
+      20 |   1000
+(2 rows)
+
+--
+-- initial queries 
+--
+-- do a simple equivalent of an UPDATE join
+BEGIN;
+MERGE INTO Stock USING Buy ON Stock.item_id = Buy.item_id
+ WHEN MATCHED THEN UPDATE SET balance = balance + Buy.volume
+;
+SELECT * FROM Stock ORDER BY item_id;
+ item_id | balance 
+---------+---------
+      10 |    3200
+      20 |    1900
+(2 rows)
+
+ROLLBACK;
+-- do a simple equivalent of an INSERT SELECT
+BEGIN;
+MERGE INTO Stock USING Buy ON Stock.item_id = Buy.item_id
+ WHEN NOT MATCHED THEN INSERT VALUES (Buy.item_id, Buy.volume)
+;
+SELECT * FROM Stock ORDER BY item_id;
+ item_id | balance 
+---------+---------
+      10 |    2200
+      20 |    1900
+      30 |     300
+(3 rows)
+
+ROLLBACK;
+-- now the classic UPSERT
+BEGIN;
+MERGE INTO Stock USING Buy ON Stock.item_id = Buy.item_id
+ WHEN MATCHED THEN UPDATE SET balance = balance + Buy.volume
+ WHEN NOT MATCHED THEN INSERT VALUES (Buy.item_id, Buy.volume)
+;
+SELECT * FROM Stock ORDER BY item_id;
+ item_id | balance 
+---------+---------
+      10 |    3200
+      20 |    1900
+      30 |     300
+(3 rows)
+
+ROLLBACK;
+--
+-- Non-standard functionality
+-- 
+-- a MERGE with DELETE action, which is not allowed in Standard. 
+-- Extra qualifications are allowed in each WHEN clause.
+BEGIN;
+MERGE INTO Stock USING Sale ON Stock.item_id = Sale.item_id
+   WHEN MATCHED AND balance - volume > 0 THEN UPDATE SET balance = balance - volume
+   WHEN MATCHED THEN DELETE; 
+;
+SELECT * FROM Stock ORDER BY item_id;
+ item_id | balance 
+---------+---------
+      20 |     900
+(1 row)
+
+ROLLBACK;
+-- The DO NOTHING action is another extension for MERGE. 
+-- rows specified by DO NOTHING are ignored  
+BEGIN;
+MERGE INTO Stock USING Sale ON Stock.item_id = Sale.item_id
+  WHEN MATCHED AND balance - volume > 0 THEN DO NOTHING
+  WHEN MATCHED THEN DELETE
+;
+SELECT * FROM Stock ORDER BY item_id;
+ item_id | balance 
+---------+---------
+      20 |    1900
+(1 row)
+
+ROLLBACK;
+-- DO NOTHING is the default action for non-matching rows that do not 
+-- activate any WHEN clause. They are just ignored
+BEGIN;
+MERGE INTO Stock USING Sale ON Stock.item_id = Sale.item_id
+   WHEN MATCHED AND balance - volume > 100000 THEN UPDATE SET balance = balance - volume
+;
+SELECT * FROM Stock ORDER BY item_id;
+ item_id | balance 
+---------+---------
+      10 |    2200
+      20 |    1900
+(2 rows)
+
+ROLLBACK;
+-- Prepare the test data to generate multiple matching rows for a single target
+INSERT INTO Buy values(10, 400);
+SELECT * FROM Buy ORDER BY item_id;
+ item_id | volume 
+---------+--------
+      10 |   1000
+      10 |    400
+      30 |    300
+(3 rows)
+
+-- we now have a duplicate key in Buy, so when we join to
+-- Stock we will generate 2 matching rows, not one.
+-- According to standard this command should fail.  
+-- But it succeeds in PostgreSQL implementation by simply ignoring the second
+BEGIN;
+MERGE INTO Stock USING Buy ON Stock.item_id = Buy.item_id
+ WHEN MATCHED THEN UPDATE SET balance = balance + Buy.volume
+;
+SELECT * FROM Stock ORDER BY item_id;
+ item_id | balance 
+---------+---------
+      10 |    3200
+      20 |    1900
+(2 rows)
+
+ROLLBACK;
+--
+-- More complicated query
+--
+-- The source table of MERGE could be a SELECT clause
+BEGIN;
+MERGE INTO Stock USING
+		(SELECT Buy.item_id, (Buy.volume - Sale.volume) as v
+		FROM Buy, Sale
+		WHERE Buy.item_id = Sale.item_id) 
+        	AS BS
+	ON Stock.item_id = BS.item_id
+ WHEN MATCHED THEN UPDATE SET balance = balance + BS.v
+;	
+SELECT * FROM Stock ORDER BY item_id;
+ item_id | balance 
+---------+---------
+      10 |    1000
+      20 |    1900
+(2 rows)
+
+ROLLBACK;
+-- Subplan/sublinks can be used in MERGE actions
+-- Create a table for sublink.
+CREATE TABLE Extra (item_id int, volume int);
+INSERT INTO Extra VALUES (10, 20);
+INSERT INTO Extra VALUES (10, -7);
+INSERT INTO Extra VALUES (20, 16);
+INSERT INTO Extra VALUES (20, 5);
+INSERT INTO Extra VALUES (30, 9);
+-- The following query sum-up the volumes in Extra table and upinsert the Stock.
+BEGIN;
+MERGE INTO Stock USING Buy ON Stock.item_id = Buy.item_id
+ WHEN MATCHED THEN UPDATE SET 
+      balance = balance + Buy.volume + 
+      	(SELECT sum(volume) FROM Extra WHERE Extra.item_id = Buy.item_id)
+ WHEN NOT MATCHED THEN INSERT VALUES 
+     (Buy.item_id, Buy.volume + 
+     	(SELECT sum(volume) FROM Extra WHERE Extra.item_id = Buy.item_id))
+;
+SELECT * FROM Stock ORDER BY item_id;
+ item_id | balance 
+---------+---------
+      10 |    3213
+      20 |    1900
+      30 |     309
+(3 rows)
+
+ROLLBACK;
diff --git a/src/test/regress/parallel_schedule b/src/test/regress/parallel_schedule
index 191d1fe..2551b2a 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 80a9881..e7d7fae 100644
--- a/src/test/regress/serial_schedule
+++ b/src/test/regress/serial_schedule
@@ -123,4 +123,5 @@ 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..5cdb5db
--- /dev/null
+++ b/src/test/regress/sql/merge.sql
@@ -0,0 +1,135 @@
+-- MERGE --
+
+--  
+-- create basic tables for test, and insert some source rows to work from
+--
+--The Stock table, which records the amount of each item on hand.
+CREATE TABLE Stock(item_id int UNIQUE, balance int);
+INSERT INTO Stock VALUES (10, 2200);
+INSERT INTO Stock VALUES (20, 1900);
+SELECT * FROM Stock;
+
+--The Buy table, which records the amount we bought today for each item.
+CREATE TABLE Buy(item_id int, volume int);
+INSERT INTO Buy values(10, 1000);
+INSERT INTO Buy values(30, 300);
+SELECT * FROM Buy;
+
+--The Sale table, which records the amount we sold today for each item.
+CREATE TABLE Sale(item_id int, volume int);
+INSERT INTO Sale VALUES (10, 2200);
+INSERT INTO Sale VALUES (20, 1000);
+SELECT * FROM Sale;
+
+--
+-- initial queries 
+--
+-- do a simple equivalent of an UPDATE join
+BEGIN;
+MERGE INTO Stock USING Buy ON Stock.item_id = Buy.item_id
+ WHEN MATCHED THEN UPDATE SET balance = balance + Buy.volume
+;
+SELECT * FROM Stock ORDER BY item_id;
+ROLLBACK;
+
+-- do a simple equivalent of an INSERT SELECT
+BEGIN;
+MERGE INTO Stock USING Buy ON Stock.item_id = Buy.item_id
+ WHEN NOT MATCHED THEN INSERT VALUES (Buy.item_id, Buy.volume)
+;
+SELECT * FROM Stock ORDER BY item_id;
+ROLLBACK;
+
+-- now the classic UPSERT
+BEGIN;
+MERGE INTO Stock USING Buy ON Stock.item_id = Buy.item_id
+ WHEN MATCHED THEN UPDATE SET balance = balance + Buy.volume
+ WHEN NOT MATCHED THEN INSERT VALUES (Buy.item_id, Buy.volume)
+;
+SELECT * FROM Stock ORDER BY item_id;
+ROLLBACK;
+
+--
+-- Non-standard functionality
+-- 
+-- a MERGE with DELETE action, which is not allowed in Standard. 
+-- Extra qualifications are allowed in each WHEN clause.
+BEGIN;
+MERGE INTO Stock USING Sale ON Stock.item_id = Sale.item_id
+   WHEN MATCHED AND balance - volume > 0 THEN UPDATE SET balance = balance - volume
+   WHEN MATCHED THEN DELETE; 
+;
+SELECT * FROM Stock ORDER BY item_id;
+ROLLBACK;
+
+-- The DO NOTHING action is another extension for MERGE. 
+-- rows specified by DO NOTHING are ignored  
+BEGIN;
+MERGE INTO Stock USING Sale ON Stock.item_id = Sale.item_id
+  WHEN MATCHED AND balance - volume > 0 THEN DO NOTHING
+  WHEN MATCHED THEN DELETE
+;
+SELECT * FROM Stock ORDER BY item_id;
+ROLLBACK;
+
+-- DO NOTHING is the default action for non-matching rows that do not 
+-- activate any WHEN clause. They are just ignored
+BEGIN;
+MERGE INTO Stock USING Sale ON Stock.item_id = Sale.item_id
+   WHEN MATCHED AND balance - volume > 100000 THEN UPDATE SET balance = balance - volume
+;
+SELECT * FROM Stock ORDER BY item_id;
+ROLLBACK;
+
+-- Prepare the test data to generate multiple matching rows for a single target
+INSERT INTO Buy values(10, 400);
+SELECT * FROM Buy ORDER BY item_id;
+
+-- we now have a duplicate key in Buy, so when we join to
+-- Stock we will generate 2 matching rows, not one.
+-- According to standard this command should fail.  
+-- But it succeeds in PostgreSQL implementation by simply ignoring the second
+BEGIN;
+MERGE INTO Stock USING Buy ON Stock.item_id = Buy.item_id
+ WHEN MATCHED THEN UPDATE SET balance = balance + Buy.volume
+;
+SELECT * FROM Stock ORDER BY item_id;
+ROLLBACK;
+
+--
+-- More complicated query
+--
+-- The source table of MERGE could be a SELECT clause
+BEGIN;
+MERGE INTO Stock USING
+		(SELECT Buy.item_id, (Buy.volume - Sale.volume) as v
+		FROM Buy, Sale
+		WHERE Buy.item_id = Sale.item_id) 
+        	AS BS
+	ON Stock.item_id = BS.item_id
+ WHEN MATCHED THEN UPDATE SET balance = balance + BS.v
+;	
+SELECT * FROM Stock ORDER BY item_id;
+ROLLBACK;
+
+-- Subplan/sublinks can be used in MERGE actions
+-- Create a table for sublink.
+CREATE TABLE Extra (item_id int, volume int);
+INSERT INTO Extra VALUES (10, 20);
+INSERT INTO Extra VALUES (10, -7);
+INSERT INTO Extra VALUES (20, 16);
+INSERT INTO Extra VALUES (20, 5);
+INSERT INTO Extra VALUES (30, 9);
+
+-- The following query sum-up the volumes in Extra table and upinsert the Stock.
+BEGIN;
+MERGE INTO Stock USING Buy ON Stock.item_id = Buy.item_id
+ WHEN MATCHED THEN UPDATE SET 
+      balance = balance + Buy.volume + 
+      	(SELECT sum(volume) FROM Extra WHERE Extra.item_id = Buy.item_id)
+ WHEN NOT MATCHED THEN INSERT VALUES 
+     (Buy.item_id, Buy.volume + 
+     	(SELECT sum(volume) FROM Extra WHERE Extra.item_id = Buy.item_id))
+;
+SELECT * FROM Stock ORDER BY item_id;
+ROLLBACK;