How to merge particular datatable in asp.net c#?

Question

I have three data tables in data set. want to merge first two tables.but don't delete third table.third table data also mandatory.<br />how to do it?<br />i want to insert merged table to DB.and another table to another data table to DB<br />Is It Possible.<br /><br />i explain my level best.if you don't understand my requirement improve my explanation.