fixes #676

Author: wumpz

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

@@ -53,7 +53,8 @@ public void setValues(List<Expression> values) {
 
     @Override
     public String toString() {
-        return " WHEN NOT MATCHED THEN INSERT " + PlainSelect.getStringList(columns, true, true)
+        return " WHEN NOT MATCHED THEN INSERT "
+                + (columns.isEmpty() ? "" : PlainSelect.getStringList(columns, true, true))
                 + " VALUES " + PlainSelect.getStringList(values, true, true);
     }
 }

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

@@ -945,7 +945,7 @@ MergeInsert MergeInsertClause() : {
 }
 {
     <K_WHEN> <K_NOT> <K_MATCHED> <K_THEN> 
-        <K_INSERT> "(" col=Column() { columns.add(col); } ("," col=Column() { columns.add(col); } )* ")"  <K_VALUES> 
+        <K_INSERT> ["(" col=Column() { columns.add(col); } ("," col=Column() { columns.add(col); } )* ")"]  <K_VALUES> 
            "(" exp=SimpleExpression() { expList.add(exp); } ("," exp=SimpleExpression() { expList.add(exp); } )* ")" 
     {
         mi.setColumns(columns);

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

@@ -21,9 +21,9 @@
 import net.sf.jsqlparser.JSQLParserException;
 import net.sf.jsqlparser.parser.CCJSqlParserUtil;
 import net.sf.jsqlparser.statement.Statement;
-import org.junit.Test;
 import static net.sf.jsqlparser.test.TestUtils.*;
 import static org.junit.Assert.fail;
+import org.junit.Test;
 
 /**
  *
@@ -64,6 +64,21 @@ public void testMergeIssue232() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed(sql, true);
     }
 
+    @Test
+    public void testMergeIssue676() throws JSQLParserException {
+        String sql = "merge INTO M_KC21 USING\n"
+                + "(SELECT AAA, BBB FROM I_KC21 WHERE I_KC21.aaa = 'li_kun'\n"
+                + ") TEMP ON (TEMP.AAA = M_KC21.AAA)\n"
+                + "WHEN MATCHED THEN\n"
+                + "UPDATE SET M_KC21.BBB = 6 WHERE enterprise_id IN (0, 1)\n"
+                + "WHEN NOT MATCHED THEN\n"
+                + "INSERT VALUES\n"
+                + "(TEMP.AAA,TEMP.BBB\n"
+                + ")";
+
+        assertSqlCanBeParsedAndDeparsed(sql, true);
+    }
+
     @Test
     public void testComplexOracleMergeIntoStatement() throws JSQLParserException {
         String sql = "MERGE INTO DestinationValue Dest USING\n"