title: Merge two DataTables without duplicate values for a column
body: <p>I have two DataTables like</p>
  
  <p>DataTable1(With default values)-</p>
  
  <pre>
  Tag |Alias|Value  |Type
  abc |""   |default|default
  xyz |""   |default|default
  </pre>
  
  <p>DataTable2(With actual values)-</p>
  
  <pre>
  Tag |Alias |Value  |Type
  abc |test  |12    |Real
  </pre>
  
  <p>Now if I use DataTable.Merge() I get the rows with both default and actual values for tag abc.
  I need only the actual values for a particular tag present in 2nd table, if not the default values from 1st table.
  How do i do this?</p>