C# join DataTable (support Left/Right/Full join)

 using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data;

namespace JoinDataTable
{
    public partial class frmMain : Form
    {
        DataTable table1 = null;
        DataTable table2 = null;

        public frmMain()
        {
            InitializeComponent();

            table1 = new DataTable();
            table1.Columns.Add("symbol", typeof(string));
            table1.Columns.Add("side", typeof(int));
            table1.Columns.Add("qty", typeof(int));
            table1.Rows.Add(new object[] { "HSI", -1, 9000});
            table1.Rows.Add(new object[] { "TOPIX", 1, 2000 });
            dataGridView1.DataSource = table1.DefaultView;

            table2 = new DataTable();
            table2.Columns.Add("symbol", typeof(string));
            table2.Columns.Add("side", typeof(int));
            table2.Columns.Add("qty", typeof(int));
            table2.Rows.Add(new object[] { "HSI", 1, 6000 });
            table2.Rows.Add(new object[] { "AEX", -1, 5000 });
            dataGridView2.DataSource = table2.DefaultView;

            DataTable t3 = Join(table1, table2,
                new DataColumn[] { table1.Columns[0]},
                new DataColumn[] { table2.Columns[0]},
                true, true);

            dataGridView3.DataSource = t3.DefaultView;
        }

        private DataTable Join(DataTable left, DataTable right,
            DataColumn[] leftCols, DataColumn[] rightCols,
            bool includeLeftJoin, bool includeRightJoin)
        {
            DataTable result = new DataTable("JoinResult");
            using (DataSet ds = new DataSet())
            {
                ds.Tables.AddRange(new DataTable[] { left.Copy(), right.Copy() });
                DataColumn[] leftRelationCols = new DataColumn[leftCols.Length];
                for (int i = 0; i < leftCols.Length; i++)
                    leftRelationCols[i] = ds.Tables[0].Columns[leftCols[i].ColumnName];

                DataColumn[] rightRelationCols = new DataColumn[rightCols.Length];
                for (int i = 0; i < rightCols.Length; i++)
                    rightRelationCols[i] = ds.Tables[1].Columns[rightCols[i].ColumnName];

                //create result columns
                for (int i = 0; i < left.Columns.Count; i++)
                    result.Columns.Add(left.Columns[i].ColumnName, left.Columns[i].DataType);
                for (int i = 0; i < right.Columns.Count; i++)
                {
                    string colName = right.Columns[i].ColumnName;
                    while (result.Columns.Contains(colName))
                        colName += "_2";
                    result.Columns.Add(colName, right.Columns[i].DataType);
                }

                //add left join relations
                DataRelation drLeftJoin = new DataRelation("rLeft", leftRelationCols, rightRelationCols, false);
                ds.Relations.Add(drLeftJoin);

                //join
                result.BeginLoadData();
                foreach (DataRow parentRow in ds.Tables[0].Rows)
                {
                    DataRow[] childrenRowList = parentRow.GetChildRows(drLeftJoin);
                    if (childrenRowList != null && childrenRowList.Length > 0)
                    {
                        object[] parentArray = parentRow.ItemArray;
                        foreach (DataRow childRow in childrenRowList)
                        {
                            object[] childArray = childRow.ItemArray;
                            object[] joinArray = new object[parentArray.Length + childArray.Length];
                            Array.Copy(parentArray, 0, joinArray, 0, parentArray.Length);
                            Array.Copy(childArray, 0, joinArray, parentArray.Length, childArray.Length);
                            result.LoadDataRow(joinArray, true);
                        }
                    }
                    else //left join
                    {
                        if (includeLeftJoin)
                        {
                            object[] parentArray = parentRow.ItemArray;
                            object[] joinArray = new object[parentArray.Length];
                            Array.Copy(parentArray, 0, joinArray, 0, parentArray.Length);
                            result.LoadDataRow(joinArray, true);
                        }
                    }
                }

                if (includeRightJoin)
                {
                    //add right join relations
                    DataRelation drRightJoin = new DataRelation("rRight", rightRelationCols, leftRelationCols, false);
                    ds.Relations.Add(drRightJoin);

                    foreach (DataRow parentRow in ds.Tables[1].Rows)
                    {
                        DataRow[] childrenRowList = parentRow.GetChildRows(drRightJoin);
                        if (childrenRowList == null || childrenRowList.Length == 0)
                        {
                            object[] parentArray = parentRow.ItemArray;
                            object[] joinArray = new object[result.Columns.Count];
                            Array.Copy(parentArray, 0, joinArray,
                                joinArray.Length - parentArray.Length, parentArray.Length);
                            result.LoadDataRow(joinArray, true);
                        }
                    }
                }

                result.EndLoadData();
            }

            return result;
        }

        private void button1_Click(object sender, EventArgs e)
        {

        }
    }
}