Adding Two Data Table using Uniqe Ids Join

  DataTable dt1 = new DataTable("Table1");  
     DataTable dt2 = new DataTable("Table2");  
     DataSet ds = new DataSet("DataSet");  
     dt1.Columns.Add("Eno", typeof(Int32));  
     dt1.Columns.Add("Ename", typeof(String));  
     dt1.Columns.Add("Salary", typeof(Double));  
     dt1.Columns.Add("Deptno", typeof(Int32));  
     dt1.PrimaryKey = new DataColumn[] { dt1.Columns["Eno"] };  
     dt2.Columns.Add("Deptno", typeof(Int32));  
     dt2.Columns.Add("Dname", typeof(String));  
     dt2.PrimaryKey = new DataColumn[] { dt2.Columns["Deptno"] };  
     ds.Tables.Add(dt1);  
     ds.Tables.Add(dt2);  
     // Loading data into dt1, dt2:  
     object[] o1 = { 1, "Ravi", 50000.50, 10 };  
     object[] o2 = { 2, "Raj", 4000.50, 20 };  
     object[] o3 = { 3, "Joni", 10000.50, 10 };  
     object[] c1 = { 10, "MFG" };  
     object[] c2 = { 20, "EAS" };  
     object[] c3 = { 30, "E&U" };  
     object[] c4 = { 40, "PES" };  
     dt2.Rows.Add(c1);  
     dt2.Rows.Add(c2);  
     dt2.Rows.Add(c3);  
     dt2.Rows.Add(c4);  
     dt1.Rows.Add(o1);  
     dt1.Rows.Add(o2);  
     dt1.Rows.Add(o3);  
     DataRelation drel = new DataRelation("EquiJoin", dt2.Columns["Deptno"], dt1.Columns["Deptno"]);  
     ds.Relations.Add(drel);  
     DataTable jt = new DataTable("Joinedtable");  
     jt.Columns.Add("Eno", typeof(Int32));  
     jt.Columns.Add("Ename", typeof(String));  
     jt.Columns.Add("Salary", typeof(Double));  
     jt.Columns.Add("Deptno", typeof(Int32));  
     jt.Columns.Add("Dname", typeof(String));  
     ds.Tables.Add(jt);  
     foreach (DataRow dr in ds.Tables["Table1"].Rows)  
     {  
       DataRow parent = dr.GetParentRow("EquiJoin");  
       DataRow current = jt.NewRow();  
       // Just add all the columns' data in "dr" to the New table.  
       for (int i = 0; i < ds.Tables["Table1"].Columns.Count; i++)  
       {  
         current[i] = dr[i];  
       }  
       // Add the column that is not present in the child, which is present in the parent.  
       current["Dname"] = parent["Dname"];  
       jt.Rows.Add(current);  
     }  
     GridView1.Visible = true;  

finally bind gridiew
      

  GridView1.DataSource = ds.Tables["Joinedtable"];  
  GridView1.DataBind();  

How we Get the Data Table Unique IDs Rows into another Data Table in c# for ASP.net for Grid View Binding:

  string[] FinalIDs = { };  
  DataTable dt1 = new DataTable();  
  DataTable dt2 = new DataTable();  
  FinalIDs = IDs.Distinct().ToArray();  
           int i = 0;  
       foreach (string Item in FinalIDs)  
       {  
         if (i == 0)  
         {  
           dt1.DefaultView.RowFilter = "Someid='" + Item + "'";  
           dt2 = (dt1.DefaultView).ToTable();  
         }  
         else  
         {  
           dt1.DefaultView.RowFilter = "Someid='" + Item + "'";  
           dt2.ImportRow((dt1.DefaultView).ToTable().Rows[0]);  
         }  
         i++;  
          }  
       i = 0;  

finally you can bind dt2 data table to any grid directly..

 gridView2.DataSource = dt2;  
 gridView2.DataBind();