MySqlDataReader读数据库TIME类型字段的问题


using (MySqlCommand objSqlCmd = m_DBMonConn.CreateCommand())
            {
                objSqlCmd.CommandText = sQueryCmd;
                MySqlDataReader dr = null;//防止后面未赋值错误
                try
                {
                    dr = objSqlCmd.ExecuteReader();
                    if (dr.Read())
                    {
                        str += dr.GetDateTime(dr.GetOrdinal("DATE")).ToShortDateString();
                        str += " ";
                        //str += dr.GetDateTime(dr.GetOrdinal("TIME")).ToShortTimeString();
                        str += dr.GetString(dr.GetOrdinal("TIME"));
                    }
                    Console.WriteLine(str);
                }
                catch (MySqlException ex) {
                    MessageBox.Show(ex.Message, "acqDBLastDateTime");
                }
                finally {
                    dr.Close();
                }
                
                //dr.Close();
            }上述代码
str += dr.GetDateTime(dr.GetOrdinal("TIME")).ToShortTimeString();会报System.ArgumentOutOfRangeException
改成dr.GetString反而OK，TIME字段数据类型也是TIME
何解？