Merging two Datatables into One C# -

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i have simple issue yet can't resolve , issue each time merge 2 datatables merge comes out funny looking , table 1 goes on top of table 2 , know because didn't set primary key of column ,but when did error because having duplicate values in enitity column .how pass , knowing duplicate values occur in primary key column 

private void button1_click(object sender, eventargs e)             {                 datatable merge = new datatable() ;                 merge.merge(t1());                 merge.merge(t2());                 gridcontrol1.datasource = merge.defaultview;             }             public datatable t1()             {                 datacolumn col;                  datatable d = new datatable();                 d.columns.add("enitity");                  d.primarykey = new datacolumn[] { d.columns["enitity"] };                 //d.primarykey = null;                 d.columns.add("variable");                 d.rows.add(new string []{"k1","100"});                 d.rows.add(new string[] { "k1", "200" });                 d.rows.add(new string[] { "k3", "300" });                 d.rows.add(new string[] { "k4", "400" });                 d.rows.add(new string[] { "k6", "500" });                 d.rows.add(new string[] { "k5", "600" });                 return d;             }             public datatable t2()             {                 datacolumn col;                 datatable d = new datatable();                 d.columns.add("enitity");                  d.primarykey = new datacolumn[] { d.columns["enitity"] };                 d.primarykey = null;                 d.columns.add("variable2");                 d.rows.add(new string[] { "k1", "1000" });                 d.rows.add(new string[] { "k2", "2000" });                 d.rows.add(new string[] { "k3", "3000" });                 d.rows.add(new string[] { "k4", "4000" });                 d.rows.add(new string[] { "k5", "5000" });                 d.rows.add(new string[] { "k7", "6000" });                 return d;              }

this how merge looks 

enitty      variable       variable 2 ---------     -----        ----------- k1              . k2              . k3              . k4              . . . . k1                             . k2                             . k3                             . k4 . . .

as stated above, cannot set primary key because have duplicate values. you're better off using linq, like:

        datatable mynewdatatable = new datatable();         mynewdatatable.columns.add("enitity", typeof(string));         mynewdatatable.columns.add("variable", typeof(string));         mynewdatatable.columns.add("variable2", typeof(string));         var results = (from d1 in t1().asenumerable()                        join d2 in t2().asenumerable()                              on d1.field<string>("enitity") equals d2.field<string>("enitity")                        select mynewdatatable.loaddatarow( new object[] { d1.field<string>("enitity"), d1.field<string>("variable"), d2.field<string>("variable2") }, true) );         mynewdatatable = results.copytodatatable<datarow>();

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