SagaDB.MYSQLUserDB.WriteUser C# (CSharp) Method

        public void WriteUser(User user)
        {
            string sqlstr;
            DataRowCollection result = null;
            if (user != null && this.isConnected()==true )
            {
                sqlstr = "SELECT * FROM `login` WHERE `username`='" + user.Name + "'";
                try
                {
                    result = SQLExecuteQuery(sqlstr);
                }
                catch (Exception)
                {
                    Console.WriteLine("Error: can't get user from database");
                    this.isconnected = false;
                    throw new Exception("can't get user from database");
                }
                if (result.Count > 0)
                {
                    sqlstr = string.Format("UPDATE `login` set `password`='{0}',`sex`='{1}',`lastlogin`='{2}' WHERE `username`='{3}'", user.Password, (int)user.Sex, user.lastLogin,user.Name );
                    try
                    {
                        MySqlHelper.ExecuteNonQuery(db, sqlstr, null);

                    }
                    catch (Exception)
                    {
                        Console.WriteLine("Error: can't create new user in database");
                        this.isconnected = false;
                        throw new Exception("can't create new user in database");
                    }
                }
                else
                {
                    sqlstr = string.Format("INSERT INTO `login`(`username`,`password`,`sex`,`lastlogin`) VALUES ('{0}','{1}','{2}','{3}')",user.Name, user.Password,(int)user.Sex, user.lastLogin);
                    try
                    {
                        SQLExecuteNonQuery(sqlstr);
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine("Error: can't create new user in database:" + ex.Message );
                        throw new Exception("can't create new user in database");
                    }
                }
            }
        }