title: C# Join two DataTables Linq to obtain flatten results
body: <p>There are 2 datatables structured in this way:</p>
  
  <ul>
  <li>First DataTAble has two cols: Customer, Email_Key</li>
  <li>Second DataTAble has two cols: IdCustomer (equals Email_Key), Email</li>
  </ul>
  
  <p>Foreach row in Dt1 can correspond many rows in Dt2 (1 to N) joining EmailKey on CustomerId, so I want to flatten result inside 1 record by using the SelectMany func. How can I achieve this?</p>