Прочетете данни от SqlDataReader

using(SqlDataReader rdr = cmd.ExecuteReader())
{
    while (rdr.Read())
    {
        var myString = rdr.GetString(0); //The 0 stands for "the 0'th column", so the first column of the result.
        // Do somthing with this rows string, for example to put them in to a list
        listDeclaredElsewhere.Add(myString);
    }
}