protected void Button1_Click(object sender, EventArgs e)
        {
            string cString = "Data Source=server;Initial Catalog=db;User ID=test;Password=test;";
            SqlConnection conn = new SqlConnection();
            conn.ConnectionString = cString;
            conn.Open();
            SqlCommand cmd = new SqlCommand();
            cmd.CommandType=CommandType.Text;
            cmd.CommandText = "select count(*) from tableName where userName=" + TextBox1.Text;
　　　　　　　　//这里的TextBox1.Text是用户名
            cmd.Connection =conn;

            int count =(int) cmd.ExecuteScalar();
            if (count>0)
            {
                Response.Write("登录成功");
            }
            else
            {
                Response.Write("登录失败");
            }
        }