变量SQL 是一个字符串. string 没有方法ExecuteScalar()

改变

variable SQL is a string. A string has no method ExecuteScalar()

change

actamttxtbox.Text = SQL.ExecuteScalar();

到

to

actamttxtbox.Text = (string)command.ExecuteScalar();

而且您不需要cmd.ExecuteNonQuery();



我已经整理了一下:

And you don''t need cmd.ExecuteNonQuery();



I''ve cleaned up a little bit:

MySqlConnection conn = new MySqlConnection("connection-string");
conn.Open();

using(MySqlCommand cmd = new MySqlCommand()){
  cmd.Connection = conn;
  cmd.CommandText = "select sum(Actual_amt) from tds";
  actamttxtbox.Text = cmd.ExecuteScalar().ToString();
}
conn.Close();