判断用户名和密码的的数据库执行代码

共同的代码：string uid = txtUser.Text.Trim().ToString();//保存登录界面输入的用户名 
        string pwd = txtPwd.Text.Trim().ToString();//保存登录界面输入的密码 
        //string constr = "server=.;database=user;uid=sa;pwd=123456;"; 
        string conStr = ConfigurationManager.ConnectionStrings["connectionString"].ToString();//取出配置文件中连接字符串 
        SqlConnection conn = new SqlConnection(conStr); 
        conn.Open();//打开数据库连接 
方法一：只使用dataadapter适配器对象 

        string sql = "select *from admin where userName='" + uid + "' and pwd='" + pwd + "'"; 
       SqlDataAdapter da = new SqlDataAdapter(sql, conn); 
        DataSet ds = new DataSet(); 
        da.Fill(ds,"admin"); 
       if (ds.Tables!=null) 
        { 
            
            Session["uid"]=uid; 
            Session["pwd"]=pwd; 
            Response.Redirect("index.aspx"); 
        } 
        else { Response.Write("<script>alert('用户名或密码错误！')</script>"); } 
方法二：使用sqlcommand命令中的ExecuteScalar()方法返回结果集中的第一行中的第一列 
        string sql = "select count(*) from admin where userName='"+uid+"' and pwd='"+pwd+"'"; 
        SqlCommand cmd = new SqlCommand(sql, conn);//构建cmd命令对象 
        int i =(int)cmd.ExecuteScalar(); 
       if (i>0) 
        { 
        Session["uid"]=uid; 
          Session["pwd"]=pwd; 
         Response.Redirect("index.aspx"); 
       }  
      else { Response.Write("<script>alert('用户名或密码错误！')</script>"); } 
方法三：使用sqlcommand命令中的ExecuteReader()方法返回SqlDataReader的结果集 
         string sql = "select *from admin where userName='" + uid + "' and pwd='" + pwd + "'"; 
         SqlDataReader sdr=cmd.ExecuteReader(); 
         sdr.Read(); 
         if (sdr.HasRows) 
        { 
           Session["uid"]=uid; 
          Session["pwd"]=pwd; 
           Response.Redirect("index.aspx"); 
        } 
        else { Response.Write("<script>alert('用户名或密码错误！')</script>"); }