MAX(id) using SqlDataReader C#

问题

How do I change this:

        using (SqlCommand myCommand = myConnection.CreateCommand())
        {
            myConnection.Open();
            myCommand.CommandText = "SELECT FormID FROM tbl_Form";
            using (SqlDataReader reader = myCommand.ExecuteReader())
            {
                while (reader.Read())
                {
                    int FormID = reader.GetInt32(reader.GetOrdinal("FormID"));
                    MessageBox.Show(FormID.ToString());
                }
            }
        }

to get MAX(FormID) ?

My natural tendency is to throw a MAX around FormID but I'm getting an IndexOutOfRange exception.

回答1:

When you select the maximum id you shouldn't use a SqlDataReader - the query returns just one item, which by default is unnamed so your existing query breaks because it expects a result named "FormID" - although you could have "fixed" your query by using "SELECT MAX(FormID) as FormId FROM tbl_Form". Instead use ExecuteScalar():

myCommand.CommandText = "SELECT MAX(FormID) FROM tbl_Form";
int maxId = Convert.ToInt32(myCommand.ExecuteScalar());

回答2:

It's been a while since I used this style of database access, but I think you just need

select max(FormID) from tbl_Form

along with a call to ExecuteScalar

来源：https://stackoverflow.com/questions/9245197/maxid-using-sqldatareader-c-sharp