关于SqlDataReader的IndexOutOfRangeException问题

Question

我是个渣学生，我希望能把StorageRec表中某一条件下（WeapName=XXX）的列StoCount做求和计算后返回一个int值，用作以后的计算 
以下是我的代码：
        public static int Count(Entity.WeaponInfo Count)
        {
            SqlConnection conn = new SqlConnection("Server=.; Integrated Security=True; Database=WeaponSalesMng");
            SqlCommand cmd = new SqlCommand("select sum(StoCount) from StorageRec where WeapName=@WeapName", conn);
            cmd.Parameters.Add(new SqlParameter("@WeapName", Count.Name));
            conn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            dr.Read();
            int count = (int)dr["StoCount"];//未处理 IndexOutOfRangeException
            return count;
        }
求解

Answer 1

cmd.ExecuteScalar();
返回结果集的第一行第一列，直接用这个就可以了

Answer 2

           SqlCommand cmd = new SqlCommand("select sum(StoCount) as StoCount from StorageRec where WeapName=@WeapName", conn);
            cmd.Parameters.Add(new SqlParameter("@WeapName", Count.Name));
            conn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            if (dr.Read())
{
            int count = (int)dr["StoCount"];
}

Answer 3

不过如1楼所说，这种sum(StoCount) 的sql语句只有一个行一个列，应该用ExecuteScalar           SqlCommand cmd = new SqlCommand("select sum(StoCount) from StorageRec where WeapName=@WeapName", conn);
            cmd.Parameters.Add(new SqlParameter("@WeapName", Count.Name));
            conn.Open();int count=(int)cmd.ExecuteScalar();

Answer 4

这样也可以：       public static int Count(Entity.WeaponInfo Count)
        {
            SqlConnection conn = new SqlConnection("Server=.; Integrated Security=True; Database=WeaponSalesMng");
            SqlCommand cmd = new SqlCommand("select sum(StoCount) from StorageRec where WeapName=@WeapName", conn);
            cmd.Parameters.Add(new SqlParameter("@WeapName", Count.Name));
            conn.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            if (!dr.Read()) return 0;
            int count = (int)dr[0];//
            return count;
        }

Answer 5

这样查询，列名就变成了 sum(StoCount) 而不再是 StoCount
(int)dr[0] 按索引查找，或
(int)cmd.ExecuteReader() 返回第一行第一列的值