using System;

using System.Text;

using System.Collections.Generic;

using System.Data;

​

​

public class Program

{

    public static void Main()

    {

        var rightDt = new DataTable();

        rightDt.Columns.Add("Foo");

        rightDt.Columns.Add("Bar", typeof(int));

        rightDt.Columns.Add("Baz");

        rightDt.Rows.Add("John", 1, "R");

        rightDt.Rows.Add("Mark", 2, "R");

        rightDt.Rows.Add("Luke", 3, "R");

        var leftDt = new DataTable();

        leftDt.Columns.Add("Wit");

        leftDt.Columns.Add("Woo", typeof(int));

        leftDt.Columns.Add("Baz");

        leftDt.Rows.Add("Mark", 2, "L");

        leftDt.Rows.Add("Luke", 3, "R");

        leftDt.Rows.Add("Mary", 4, "L");

​

​

        var allKeys = new HashSet<(string, int)>();

​

        var rIndex = new Dictionary<(string, int), DataRow>();

​

        foreach(DataRow r in rightDt.Rows){

          var key = (r.Field<string>("Foo"), r.Field<int>("Bar"));

          rIndex[key] = r;

          allKeys.Add(key);

        }

​

        var lIndex = new Dictionary<(string, int), DataRow>();

​

        foreach(DataRow r in leftDt.Rows){

          var key = (r.Field<string>("Wit"), r.Field<int>("Woo"));

          lIndex[key] = r;

          allKeys.Add(key);

        }

​

        foreach(var k in allKeys){

          var inL = lIndex.ContainsKey(k);

          var inR = rIndex.ContainsKey(k);

​

          if(inL && inR){

            var updateRo = lIndex[k]; //update the db using this datarow, or maybe don't bother if other data is already the same

            var toUpdate = rIndex[k]; //the update target

            if(toUpdate["Baz"].ToString() == updateRo["Baz"].ToString())

              Console.WriteLine("dont update" + k.ToString() + " because other data is same");

            else

              Console.WriteLine("update" + k.ToString());

          } else if(inL){

            var insertRo = lIndex[k]; //insert this row to the db

            Console.WriteLine("insert" + k.ToString());

          } else {

            var deleteRo = rIndex[k]; //delete this row from the db

            Console.WriteLine("delete" + k.ToString());

          }

        }

    }

}