Use Linq-to-DataSets to query against (typed) DataTables and DataSets using the LINQ syntax : LINQ « ADO.net Database « ASP.NET Tutorial

<%@ Page Language="C#" 
         AutoEventWireup="true" 
         CodeFile="Default.aspx.cs" 
         Inherits="Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Linq-to-DataSets</title>
</head>
<body>
    <form id="form1" runat="server">
        <div id="pageContent">
            <asp:Button ID="Button1" runat="server" Text="First 10 Days of Jan98" onclick="Button1_Click" />
            <asp:GridView ID="GridView1" runat="server">
            </asp:GridView>    
        </div>
    </form>
</body>
</html>

File: Default.aspx.cs

using System;
using System.Data;
using System.Data.SqlClient;
using System.Collections;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Xml.Linq;

public partial class Default : System.Web.UI.Page
{
    protected void Button1_Click(object sender, EventArgs e)
    {
        string connString = "SERVER=(local);DATABASE=northwind;Trusted_Connection=yes;";
        string cmd = "SELECT * FROM customers;SELECT * FROM orders";
        SqlDataAdapter adapter = new SqlDataAdapter(cmd, connString);
        DataSet ds = new DataSet();
        adapter.Fill(ds);

        var customers = ds.Tables[0].AsEnumerable();
        var orders = ds.Tables[1].AsEnumerable();

        var data = from o in orders
                   join c in customers
                   on o.Field<string>("CustomerID") equals c.Field<string>("CustomerID")
                   where o.Field<DateTime>("OrderDate").Year == 1998 &&
                         o.Field<DateTime>("OrderDate").Month == 1 &&
                         o.Field<DateTime>("OrderDate").Day < 10
                   select new {OrderID=o.Field<int>("OrderID"), 
                                Company=c.Field<string>("CompanyName")};

        GridView1.DataSource = data; 
        GridView1.DataBind();
    }
}

18.50.LINQ
	18.50.1.	use Linq-to-Objects to query against .NET collections using the LINQ syntax
	18.50.2.	Use Linq-to-DataSets to query against (typed) DataTables and DataSets using the LINQ syntax
	18.50.3.	A grid with an empty data source.