c# - 如何获得 2 列的值，而不仅仅是 1 列？

Question

我想要两列的结果，而不仅仅是一列。我试过了：

MessageBox.Show(reader.GetString("traceid", "idref"));

但它不起作用。我是C#的初学者，有人可以帮忙吗？

String str = @"server=localhost;database=asianimport;userid=tera;password=******;";
MySqlConnection con = null;

try
{
    con = new MySqlConnection(str);
    con.Open(); //open the connection
    MessageBox.Show("connect " );

    String cmdText = "SELECT * FROM tracerecord limit 3";
    MySqlCommand cmd = new MySqlCommand(cmdText, con);
    MySqlDataReader reader = cmd.ExecuteReader();

    while (reader.Read())
    {
        MessageBox.Show(reader.GetString("traceid", "idref"));
    }
}

Answer 1

执行GetString()两次，每个字段一次：

while (reader.Read())
{
    String traceID = reader.GetString("traceid");
    String idRef = reader.GetString("idref");
    MessageBox.Show(traceID + " - " + idRef);
}

Answer 2

reader.GetString() 仅从当前记录的一列返回结果。将它们分别用于具有串联的每个列：

MessageBox.Show(reader.GetString("traceid")+ " "+reader.GetString("idref"));