using (SqlConnection conn = new SqlConnection("连接字符串"))
            {
                SqlCommand cmd = new SqlCommand("select replace(列名,'号','') as col1 from 表名", conn);
                conn.Open();
                List<int> list = new List<int>();
                using (SqlDataReader sdr = cmd.ExecuteReader())
                {
                    while (sdr.Read())
                    {
                        list.Add(Convert.ToInt32(sdr["col1"]));
                    }
                }
                if (list.Count > 0)
                {
                    list.Sort();
                    bool[] array = new bool[list[list.Count - 1]];
                    foreach (int i in list)
                        array[i - 1] = true;
                    Console.WriteLine("没有的号有：");
                    for (int i = 0; i < array.Length; i++)
                    {
                        if (!array[i])
                            Console.WriteLine(i + 1);
                    }
                }

            }

------解决方案--------------------
处理成数字数组，然后循环比较看有没有呗，最笨的办法了
C# code

string str = "1号，3号，6号";
            str=str.Replace("号", "");
            int[] arr = str.Split('，').OrderBy( p=>p ).Select(p1=>int.Parse(p1)).ToArray();

            List<int> result = new System.Collections.Generic.List<int>(); 
            for (int i = arr[0]; i < arr[arr.Length - 1]; i++)
            {
                if (!arr.Contains(i))
                {
                    result.Add(i);
                }
            }

------解决方案--------------------
C# code

 static void Main(string[] args)
        {
            string[] arry = { "1号", "3号", "5号", "10号","100号" };
            List<string> list = new List<string>();

            int len = int.Parse(arry.Last().Substring(0, arry.Length - 2));

            for (int i = 1; i < len; i++)
            {
                if (!arry.Contains(i.ToString()+"号"))
                {
                    list.Add(i.ToString());
                }
            }

            foreach (var item in list)
            {
                Console.WriteLine(item);
            }
            Console.Read();
        }

------解决方案--------------------
1,用SQL把数字查出来。 select replace(column,'号','') as col1 from table

2，用一个数组保存这个结果

3，弄一个嵌套循环，如果array[i] <>i,则取出所有 array[i]和i之间的值。