using System;

using System.Data;

using System.Xml;

using System.Linq;

using System.Data.DataSetExtensions;

using System.Collections;

using System.Collections.Generic;

​

public class Test

{

    public static void Main()

    {

        var Table1 = new DataTable();

        var Table2 = new DataTable();

        // Categorie

        Table1.Columns.Add("ID");

        Table1.Columns.Add("Name");

        Table1.Columns.Add("Order");

        // Services

        Table2.Columns.Add("ID");

        Table2.Columns.Add("Name");

        Table2.Columns.Add("Categorie");            

        Table1.Rows.Add(1, "Installation", 1);

        Table1.Rows.Add(2, "Betrieb", 2);

        Table1.Rows.Add(3, "Backup", 3);

        Table1.Rows.Add(4, "Test", 4);

        Table2.Rows.Add(1, "Server Installation", 1);

        Table2.Rows.Add(2, "Dokumentation", 1);

        Table2.Rows.Add(3, "Updates", 2);

        Table2.Rows.Add(4, "Migration", 2);

        Table2.Rows.Add(5, "Vollbackup", 3);

        Table2.Rows.Add(6, "Backup Postfach", 3);

​

        IEnumerable<DataRow> rows = Table2.AsEnumerable();

        DataRow cat = Table1.AsEnumerable().Where(categorie => int.Parse((string)categorie["ID"]) == 2 ).FirstOrDefault();

        Console.WriteLine(cat["Name"]);

        var query = rows.GroupBy(row => new { Categorie = row["Categorie"], Order = Table1.AsEnumerable().Where(categorie => int.Parse((string)categorie["ID"]) == int.Parse((string)row["Categorie"])).FirstOrDefault()["Order"] } );

        query = query.OrderBy(g => g.Key.Order);

        foreach (var g in query) {

            Console.WriteLine("Key: {0}", g.Key);

            foreach (var item in g)

            {

                Console.WriteLine("\t{0}, {1}", item["ID"], item["Name"]);

            }

        }

    }

}

​

​