実際にパラメータを渡す必要があります:
command.CommandText = "SELECT * FROM CUSTOMER WHERE Id = @Id;";
command.Parameters.Add("@Id", SqlDbType.Int).Value = Id;
var reader = command.ExecuteReader();
実際にパラメータを渡す必要があります:
command.CommandText = "SELECT * FROM CUSTOMER WHERE Id = @Id;";
command.Parameters.Add("@Id", SqlDbType.Int).Value = Id;
var reader = command.ExecuteReader();