Inner join 2 database วรผู้รู้ช่วยหน่อยครับ ผมมีปัญกากับการ Inner join ครับตอนนี้ผมเขียน ASP.NET(C#)

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

using System.Collections;

/// <summary>
/// Summary description for SqlDatabase
/// </summary>
public class JoinDataTable
{
    public JoinDataTable()
    {
        //
        // TODO: Add constructor logic here
        //
    }

    /// <summary>
    /// Join DataTable with DataTable.
    /// </summary>
    public static DataTable Join(DataTable LeftTable, DataTable RightTable, string LeftPrimaryColumn, string RightPrimaryColumn)
    {
        //first create the datatable columns 
        DataSet mydataSet = new DataSet();
        mydataSet.Tables.Add("  ");
        DataTable myDataTable = mydataSet.Tables[0];

        //add left table columns 
        DataColumn[] dcLeftTableColumns = new DataColumn[LeftTable.Columns.Count];
        LeftTable.Columns.CopyTo(dcLeftTableColumns, 0);

        foreach (DataColumn LeftTableColumn in dcLeftTableColumns)
        {
            if (!myDataTable.Columns.Contains(LeftTableColumn.ToString()))
                myDataTable.Columns.Add(LeftTableColumn.ToString());
        }

        //now add right table columns 
        DataColumn[] dcRightTableColumns = new DataColumn[RightTable.Columns.Count];
        RightTable.Columns.CopyTo(dcRightTableColumns, 0);

        foreach (DataColumn RightTableColumn in dcRightTableColumns)
        {
            if (!myDataTable.Columns.Contains(RightTableColumn.ToString()))
            {
                if (RightTableColumn.ToString() != RightPrimaryColumn)
                    myDataTable.Columns.Add(RightTableColumn.ToString());
            }
        }

        //add left-table data to mytable 
        foreach (DataRow LeftTableDataRows in LeftTable.Rows)
        {
            myDataTable.ImportRow(LeftTableDataRows);
        }

        ArrayList var = new ArrayList(); //this variable holds the id's which have joined 

        ArrayList LeftTableIDs = new ArrayList();
        LeftTableIDs = DataSetToArrayList(0, LeftTable);

        //import righttable which having not equal Id's with lefttable 
        foreach (DataRow rightTableDataRows in RightTable.Rows)
        {
            if (LeftTableIDs.Contains(rightTableDataRows[0]))
            {
                string wherecondition = "[" + myDataTable.Columns[0].ColumnName + "]='"
                        + rightTableDataRows[0].ToString() + "'";
                DataRow[] dr = myDataTable.Select(wherecondition);
                int iIndex = myDataTable.Rows.IndexOf(dr[0]);

                foreach (DataColumn dc in RightTable.Columns)
                {
                    if (dc.Ordinal != 0)
                        myDataTable.Rows[iIndex][dc.ColumnName.ToString().Trim()] =
                rightTableDataRows[dc.ColumnName.ToString().Trim()].ToString();
                }
            }
            else
            {
                int count = myDataTable.Rows.Count;
                DataRow row = myDataTable.NewRow();
                row[0] = rightTableDataRows[0].ToString();
                myDataTable.Rows.Add(row);
                foreach (DataColumn dc in RightTable.Columns)
                {
                    if (dc.Ordinal != 0)
                        myDataTable.Rows[count][dc.ColumnName.ToString().Trim()] =
                rightTableDataRows[dc.ColumnName.ToString().Trim()].ToString();
                }
            }
        }

        return myDataTable;
    }

    private static ArrayList DataSetToArrayList(int ColumnIndex, DataTable dataTable)
    {
        ArrayList output = new ArrayList();

        foreach (DataRow row in dataTable.Rows)
            output.Add(row[ColumnIndex]);

        return output;
    }
}