使用ADO.NET访问数据库

string sqlcon="Data Source=.;Initial Calalog=MySchool;User ID=sa;Pwd=.";

Connection：打开数据库连接
程序与数据库沟通的桥梁

SqlConnection con=new SqlConnection(sqlcon);
try
{
//可能发生异常的代码
con.Open();
}
catch(Exception ex)
{
//捕获异常
Console.WriteLine(ex);
}
finally
{
con.Close();
//永远都会被执行
}

Command:向数据库发送命令，提交SQL命令并从数据源中返回结果
string sql="select count(*) from Student where StudentNo='"+username+"' and LoginPwd='"+password+"'";
//向数据库发送一条SQL语句
SqlCommand command=new SqlCommand(sql,con);
//结果
int count=(int)command.ExecuteScalar();
if(count>0)
{
Console.WriteLine("登录成功");

}else
{
Console.WriteLine("查无此人");
}

class Test
    {
        string sql = "Data source = .;Initial Catalog = TestAll;User ID =Sa;PassWord=asiga0.";
        public void Show() {
            do
            {
                Console.WriteLine("****************");
                Console.WriteLine("    欢迎使用金牌查询系统   ");
                Console.WriteLine("****************");
                Console.WriteLine("1.省市金牌数 2.金牌总数");
                Console.WriteLine("请选择");
                int choose = int.Parse(Console.ReadLine());
                switch (choose)
                {
                    case 1:
                        Console.WriteLine(dan());
                        Console.WriteLine("是否继续查询");
                        string y = Console.ReadLine();
                        if (y.ToLower().Trim().Equals("y"))
                        {
                            continue;
                        }
                        break;
                    case 2:
                        Console.WriteLine(zong());
                        Console.WriteLine("是否继续查询");
                        string k = Console.ReadLine();
                        if(k.ToLower().Trim().Equals("y")){
                            continue;
                        }
                        break;
                }
                break;
            }
            while (true);
        }
        public int dan() {
            SqlConnection conn = new SqlConnection(sql);
            try
            {
                Console.WriteLine("请输入省市名称");
                string pr = Console.ReadLine();
                conn.Open();
                string s = string.Format("select number from GoldMedal where Province ='{0}'", pr);
                SqlCommand comm = new SqlCommand(s, conn);
                int a = (int)comm.ExecuteScalar();
                return a;
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                return -1;
                throw;
            }
            finally
            {
                conn.Close();
            }
        }
        public int zong() {
            SqlConnection conn = new SqlConnection(sql);
            try
            {
                conn.Open();
                string s = "select sum(number) from GoldMedal ";
                SqlCommand comm = new SqlCommand(s, conn);
                int a = (int)comm.ExecuteScalar();
                return a;
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                return -1;
                throw;
            }
            finally
            {
                conn.Close();
            }
        }
    }