compare 2 datatables and result missing data
<p>I have 2 Datatables that are quite similar but have other columnnames. The first Datatable has 4 columns and about 7000 records. The second one has also 4 columns and about 37000 records. Now i want to Display the records that are missing in the first Datatable in a third datagridview. How should I do this? I know there are a lot of code in the Internet about this but nothing has worked.</p>

<pre><code>using Microsoft.Win32; 
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.Linq;
using System.Data.OleDb;
using System.Data.Sql;
using System.Data.SqlClient;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Forms;
using System.Windows.Input;




namespace Compare
 {
  public partial class Form1 : Form
   {
    public Form1()
    {
        InitializeComponent();
    }


    DataTable ds;
    DataTable dt;

    public void btn_Click(object sender, EventArgs e)
    {
        SqlDataAdapter adapter = new SqlDataAdapter("select a.FALLZAHL, m.CODE, m.ANZ, m.STDAT From test m with (nolock) inner join test2 a with (nolock) on a.id = m.aid where m.STDAT &gt;= '2016-01-01' and m.STALT = '6363' order by a.FALLZAHL", "Server = ada; Database = sd;Trusted_Connection = True");
        ds = new DataTable(" ");
        adapter.Fill(ds);
        dataGridView1.DataSource = ds;



    }

    private void Excelsheet_Click(object sender, EventArgs e)
    {

        openFileDialog1.ShowDialog();




    }

    private void choose_Click(object sender, EventArgs e)
    {
        OpenFileDialog OpenFileDialog = new OpenFileDialog();



    }
    private string Excel03ConString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0};Extended Properties='Excel 8.0;HDR={1}'";

    private string Excel07ConString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties='Excel 8.0;HDR={0}'";







    public void openFileDialog1_FileOk(object sender, System.ComponentModel.CancelEventArgs e)
    {
        string filePath = openFileDialog1.FileName;

        string extension = Path.GetExtension(filePath);

        string header = radioButton1.Checked ? "YES" : "NO";

        string conStr, sheetName, cells;




        conStr = string.Empty;

        switch (extension)
        {



            case ".xls": //Excel 97-03

                conStr = string.Format(Excel03ConString, filePath, header);

                break;



            case ".xlsx": //Excel 07

                conStr = string.Format(Excel07ConString, filePath, header);

                break;
        }




        using (OleDbConnection con = new OleDbConnection(conStr))
        {

            using (OleDbCommand cmd = new OleDbCommand())
            {

                cmd.Connection = con;
                con.Open();

                System.Data.DataTable dtExcelSchema = con.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);

                sheetName = dtExcelSchema.Rows[0]["TABLE_NAME"].ToString();




                con.Close();







            }

        }

        using (OleDbConnection con = new OleDbConnection(conStr))
        {

            using (OleDbCommand cmd = new OleDbCommand())
            {

                using (OleDbDataAdapter oda = new OleDbDataAdapter())
                {

                    dt = new DataTable();

                    cmd.CommandText = "SELECT * From [" + sheetName + "]";

                    cmd.Connection = con;

                    con.Open();

                    oda.SelectCommand = cmd;

                    oda.Fill(dt);

                    con.Close();


                    dataGridView2.DataSource = dt; 


                }

            }

        }
    }



   private void dataGridView3_CellContentClick(object sender, DataGridViewCellEventArgs e)
    {


    }


    private void Form1_Load(object sender, EventArgs e)
    {
        /* dataGridView3.DataSource = from table1 in ds.AsEnumerable()
                      join table2 in dt.AsEnumerable() on table1.Field&lt;int&gt;("ColumnA") equals table2.Field&lt;int&gt;("ColumnA")
                      where table1.Field&lt;int&gt;("ColumnB") == table2.Field&lt;int&gt;("ColumnB") || table1.Field&lt;string&gt;("ColumnC") == table2.Field&lt;string&gt;("ColumnC") || table1.Field&lt;object&gt;("ColumnD") == table2.Field&lt;object&gt;("ColumnD")
                      select table1;
         dataGridView3.DataSource = from table1 in ds.AsEnumerable()
                      where !dataGridView3.Contains(table1)
                      select table1;
         */
    }

    public void CompareData()
    {

    }

    private void button1_Click(object sender, EventArgs e)
    {
        var dsRowCount = ds.AsEnumerable().Count();
        var dtRowCount = dt.AsEnumerable().Count();

        if (dsRowCount &gt; dtRowCount)
        {
            //Set main table to be dt as this has the least number of rows.
            dataGridView3.DataSource = NoMatches(dt, ds);
        }
        else
        {
            //Set main table to ds as this has the least number of rows OR tables have the same number of rows.
            dataGridView3.DataSource = NoMatches(ds, dt);
        }





         }

    private IEnumerable&lt;DataRow&gt; NoMatches(DataTable MainTable, DataTable SecondaryTable)
    {
        var matched = from table1 in MainTable.AsEnumerable()
                      join table2 in SecondaryTable.AsEnumerable()
                      on table1.Field&lt;string&gt;("ISH_FALLZAHL") equals table2.Field&lt;string&gt;("FAL")
                      where (table1.Field&lt;string&gt;("ML_CODE").Equals(table2.Field&lt;string&gt;("LST")))
                     || Convert.ToInt32(table1.Field&lt;Int16&gt;("ML_ANZ")) == Convert.ToInt32(table2.Field&lt;double&gt;("ST"))
                      select table1;

        return MainTable.AsEnumerable().Except(matched);
    }







       // dataGridView3.DataSource = CompareTables();


    }

    /*        public bool DatatablesAreSame()
            {



                if (ds.Rows.Count == dt.Rows.Count)

                    return true;

                foreach (DataColumn dc in ds.Columns)
                {
                    for (int i = 0; i &lt; dt.Rows.Count; i++)
                    {
                        if (ds.Rows[i][dc.ColumnName = "ISH_FALLZAHL"] != dt.Rows[i][dc.ColumnName = "FAL"])
                        {


                        }
                    }
                }

                return true;
            }

       */

/*
    private void CompareTables()
    {

        try
        {



            var dt1Records = ds.AsEnumerable().Select(e1 =&gt; new { Id = e1["ISH_FALLZAHL"].ToString(), Name = e1["FAL"].ToString() });

            var dt2Records = dt.AsEnumerable().Select(e2 =&gt; new { Id = e2["ISH_FALLZAHL"].ToString(), Name = e2["FAL"].ToString() });



            var extraRecords = dt1Records.Except(dt2Records);




            dataGridView3.DataSource = extraRecords;




        }

        catch (Exception ex)

        { }

    }

  */ 





}
</code></pre>