sqlite 保存DATATABLE ，DATATABLE有值，但是resule总是为0，没有其它异常

sqlite 保存DATATABLE ，DATATABLE有值，但是resule总是为0，没有其它错误
  
        /// <summary>
        /// 保存DataTable 
        /// </summary>
        /// <param name="dt">DataTable</param>
        /// <returns>影响的行数</returns>
        public static int SaveDataTable(DataTable dt, string tableName)
        {
            SQLiteConnection _con;
            SQLiteCommand command;
            _con = new SQLiteConnection(connectionString);
            command = _con.CreateCommand();
            SQLiteTransaction _tran = null;
            try
            {
                command.CommandText = "SELECT * FROM " + tableName;
                SQLiteDataAdapter oda = new SQLiteDataAdapter(command);
                SQLiteCommandBuilder ocb = new SQLiteCommandBuilder(oda);
                oda.InsertCommand = ocb.GetInsertCommand();
                oda.InsertCommand = ocb.GetUpdateCommand();
                oda.DeleteCommand = ocb.GetDeleteCommand();

                _con.Open();
                _tran = _con.BeginTransaction();
                command.Transaction = _tran;
                int result = oda.Update(dt);
                _tran.Commit();
                return result;
            }
            catch (Exception ex)
            {
                _tran.Rollback();
                throw new Exception("保存DataTable出错：" + ex.Message);
            }
            finally
            {
                _con.Close();
            }

        }
------解决方案--------------------
datatable没有被修改过，所以它不更新