inline mysql mult-line query using c#

/// <summary>
        /// Return an account ID based on the ordernumber and telephone;
        /// If no account already exists then generate a new account id and return its number.
        /// </summary>
        /// <param name="orderNumber"></param>
        /// <param name="telephoneNumber"></param>
        /// <returns></returns>
        public int GetAccountId(string orderNumber, string telephoneNumber)
        {
            #region Instrumentation
 
            if (log.IsInfoEnabled)
            {
                log.InfoFormat("{0}", MethodInfo.GetCurrentMethod().Name);
            }
 
            #endregion
 
            // Get the id of the account based on the order number and tel, if no id then generate a new account
            const string query = @"
                BEGIN
                    DECLARE temp_id INTEGER;
                    SET temp_id = (SELECT ID FROM Account WHERE OrderNumber=@OrderNumber AND Telephone=@Telephone LIMIT 1);
 
                    IF temp_id = 0 THEN
                      BEGIN
                        INSERT INTO Account (OrderNumber,Telephone) VALUES (@OrderNumber,@Telephone);
                        SELECT last_insert_id();
                      END;
                    ELSE
                      BEGIN
                        SELECT temp_id;
                      END;
                    END IF;
                END
                    ";
 
            MySqlDataAdapter msda = null;
 
            try
            {
               msda = new MySqlDataAdapter(query, connectionString);
               msda.SelectCommand.CommandType = CommandType.Text;
               msda.SelectCommand.Parameters.AddWithValue("@OrderNumber", orderNumber);
               msda.SelectCommand.Parameters.AddWithValue("@Telephone", orderNumber);
 
               DataTable dt = null;
 
               try
               {
                   dt = new DataTable();
                   msda.Fill(dt);
                   if (dt.Rows.Count != 0)
                   {
                       dt.Locale = CultureInfo.InvariantCulture;
 
                       return Convert.ToInt32(dt.Rows[0][0]);
                   }
                   else
                   {
                       return 0;
                   }
               }
               catch (Exception ex)
               {
                   dt.Dispose();
                   throw ex;
               }
           }
           finally
           {
               if (msda != null) msda.Dispose();
           }
        }