连接MySQL时Unknown column问题，求高手解答

import java.sql.*;

public class A
{
public static void main(String[] args)
{
try
{
Class.forName("com.mysql.jdbc.Driver");
String url="jdbc:mysql://localhost:3306/Yang";

Connection con = DriverManager.getConnection(url,"root","03allen");
Statement stmt = con.createStatement();

String query = "select * from table_1";
ResultSet rs=stmt.executeQuery(query);

while(rs.next())
{
System.out.println(rs.getString(2));

}
int a = 111111;
String b = "dd";
int c = 111;
int d = 111;
int e = 111;
String SQLOrder = "INSERT INTO table_1 VALUES("+a+","+b+","+c+","+d+","+e+")";
stmt.executeUpdate(SQLOrder);
}
catch (ClassNotFoundException e)
{
e.printStackTrace();
}
catch(SQLException e)
{
e.printStackTrace();
}

}
}

首先，数据库已经连上了，没有问题。。
数据库里五个项里，第二个类型为LONGVARCHAR。。。（MySQL里没发现String类型。。。）我在这里输入为String型的。。
出现异常：com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column "dd" in 'field list'
但是，如果我把String类型的b，改成int型的就能写入数据库，这是为什么，请高手帮忙解答