MySqlConnection DBConnection = new MySqlConnection(ConnectionString);
DBConnection.Open();
String SignInCMD = "select * from [table] where binary Username='"+usernameTextBox.Text+"' and binary Password='"+passwordTextBox.Text+"'"
MySqlCommand SignInQuery = new MySqlCommend(SignInCMD, DBConnection);
MySqlDataReader dr = SignInQuery.ExecuteReader();

if(dr.Read())
{
    MessageBox.Show(dr.GetString(1));
}
else
    MessageBox.Show("Information is not valid!");