vs链接 SQL server（Visual Studio2015 链接sql server 2014）

create table person --建立表
(
  name char(12),
  id   int primary key,
  age  int,
  sf char(16) default 'worker'
)

drop table person; --删除表格。

insert into person values('张三',110,25,'manager');
insert into person values('李四',111,25,'manager');
insert into person values('王五',101,26,default);

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection();
        con.ConnectionString = "Data Source=DESKTOP-D5KAKHM;Initial Catalog=df;Integrated Security=True ";
        con.Open();
        SqlCommand com = new SqlCommand();
        com.Connection = con;
        if(DropDownList1.SelectedValue=="all")
        com.CommandText = "select *  from person";
        else
        com.CommandText = "select * from person where sf='" + DropDownList1.SelectedValue + "'";

        SqlDataReader dr = com.ExecuteReader();
        GridView1.DataSource = dr;
        GridView1.DataBind();

    }
}