fixed #232 without correction of order of update and insert

Author: wumpz

src/main/java/net/sf/jsqlparser/statement/merge/Merge.java

@@ -112,13 +112,13 @@ public String toString() {
         StringBuilder b = new StringBuilder();
         b.append("MERGE INTO ");
         b.append(table);
-        b.append(" USING (");
+        b.append(" USING ");
         if (usingTable != null) {
             b.append(usingTable.toString());
         } else if (usingSelect != null) {
-            b.append(usingSelect.toString());
+            b.append("(").append(usingSelect.toString()).append(")");
         }
-        b.append(")");
+        
         if (usingAlias != null) {
             b.append(usingAlias.toString());
         }

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -582,10 +582,10 @@ Statement Merge() : {
 }
 {
     <K_MERGE> <K_INTO> table=TableWithAlias() { merge.setTable(table); }
-    <K_USING> "(" 
+    <K_USING> 
         ( table=Table() { merge.setUsingTable(table); } 
-            | select=SubSelect() { merge.setUsingSelect(select); } )
-    ")" [ alias = Alias() { merge.setUsingAlias(alias); } ] <K_ON> 
+            | "(" select=SubSelect() { merge.setUsingSelect(select); } ")" )
+     [ alias = Alias() { merge.setUsingAlias(alias); } ] <K_ON> 
        "(" condition = Condition() { merge.setOnCondition(condition); } ")"
 
     [ LOOKAHEAD(2) update = MergeUpdateClause() { merge.setMergeUpdate(update); } ]

src/test/java/net/sf/jsqlparser/test/merge/MergeTest.java

@@ -50,4 +50,16 @@ public void testOracleMergeIntoStatement() throws JSQLParserException {
 
         assertSqlCanBeParsedAndDeparsed(sql, true);
     }
+    
+    @Test
+    public void testMergeIssue232() throws JSQLParserException {
+        String sql = "MERGE INTO xyz using dual " +
+                        "ON ( custom_id = ? ) " +
+                        "WHEN matched THEN " +
+                        "UPDATE SET abc = sysdate " +
+                        "WHEN NOT matched THEN " +
+                        "INSERT (custom_id) VALUES (?)";
+                        
+        assertSqlCanBeParsedAndDeparsed(sql, true);
+    }
 }