串口接收，数据库插入问题，求助
串口接收代码：

private static void DataReceviedHandler(
                        object sender,
                        SerialDataReceivedEventArgs e)
        {
            SerialPort sp = (SerialPort)sender;
            string indata = sp.ReadExisting();
            insertStr += indata;
            
            foreach (char ch in insertStr)
            {
                if (ch != 'E' && ch != 'S'&& ch != 'o')
                {
                    usingStr += ch;
                }
            }

            
            string RealName = "";
            switch (usingStr)
            {
                case "2011072069\0":
                    RealName = "a";
                    break;
                case "2010073065\0":
                    RealName = "b";
                    break;
                case "2011072069":
                    RealName = "a";
                    break;
                case "2010073065":
                    RealName = "b";
                    break;
 default:
                    break;
            } 
 

            if (usingStr.Length == 11 || usingStr.Length == 10)//  && already == false
            {
                if (insertStr[0] == 'E')
                {
                    string Sqlcom = "INSERT INTO tb_out(RealName, Num, Date) VALUES('" + RealName + "'," + "'" + usingStr + "', GetDate());";
                    ExecuteSQL(Sqlcom);                   
                }
                if (insertStr[0] == 'S')
                {
                    string Sqlcom = "INSERT INTO tb_in(RealName, Num, Date) VALUES('" + RealName + "'," + "'" + usingStr + "', GetDate());";
                    ExecuteSQL(Sqlcom);
                    
                }
            }
            usingStr = "";
        }

ExecuteSQL代码如下：

public static void ExecuteSQL(string SQLwords)
        {
            //执行插入、删除、更新的函数
            string myConStr = "user id=sa; password=lzr666;";
            myConStr += "Initial Catalog = AccessControl; Server=PC2012050719LFQ;";
            myConStr += "Connect Timeout = 10";

            SqlConnection myCon = new SqlConnection(myConStr);
            myCon.Open();
            SqlCommand myCom = new SqlCommand();
            myCom.CommandType = CommandType.Text;
            myCom.CommandText = SQLwords;
            myCom.Connection = myCon;
            try
            { 
 
                myCom.ExecuteNonQuery();
            }
            catch
            {
            }
            myCon.Close();
        }

每次程序都能接收到数据，但是在插入数据库的时候只能插入2次，就不能插入了，只有关闭程序再打开，又能插入2次
第一次都会同时插入2条相同的数据

就这个问题，感谢各位大神了
[解决办法]
总觉得你执行SQL的条件很难懂：两个if，一个是用usingStr，一个是用insertStr,而前者又是根据后者生成的