操作数据库的几种写法：

(1)   string sqlconnection = ConfigurationManager.AppSettings["CeShiConn2"];
            SqlConnection mysqlconnection = new SqlConnection(sqlconnection);
            string sql = "Select * from News ";
            mysqlconnection.Open();
            SqlCommand mycommand = new SqlCommand();
            mycommand.Connection = mysqlconnection;
            mycommand.CommandText = sql;
            SqlDataAdapter myadapter = new SqlDataAdapter();
            myadapter.SelectCommand = mycommand;
            DataSet ds = new DataSet();
            myadapter.Fill(ds, "NewsTable1");
            this.GridView1.DataSource = ds.Tables["NewsTable1"];
            this.GridView1.DataBind();

(2)

 //try
            //{
            //    using (SqlConnection mysqlconnection = new SqlConnection(ConfigurationManager.ConnectionStrings["CeShiConn"].ToString()))   //引用using好处只需将链接打开不用写关闭链接的代码就会释放资源
            //    {
            //        mysqlconnection.Open();
            //        string sql = "select * from News";
            //        SqlDataAdapter adapter = new SqlDataAdapter(sql, mysqlconnection);
            //        DataSet ds = new DataSet();
            //        adapter.Fill(ds, "NewsTable");
            //        this.GridView1.DataSource = ds.Tables["NewsTable"];
            //        this.DataBind();
            //        if (ds.Tables[0].Rows.Count > 0)
            //        {
            //            Response.Write("<script> window.alert('登陆成功!')</script>");
            //        }
            //    }
            //    this.Label1.Text = "数据库连接完毕";
            //}
            //catch
            //{

            //    Response.Write("<script> window.alert('登录失败,请重新登录!')</script>");
            //}

(3)   int s = Convert.ToInt32(cmd.ExecuteScalar());