private void AddConstraint ( DataTable myTable ) {
   UniqueConstraint myUniqueConstraint;
   // assuming a column named "UniqueColumn" exists, and its Unique property is true.
   myUniqueConstraint = new UniqueConstraint ( myTable.Columns [ "UniqueColumn" ] );
   myTable.Constraints.Add ( myUniqueConstraint );
}

Private Sub AddConstraint ( myTable As DataTable )
    Dim myUniqueConstraint As UniqueConstraint
    ' assuming a column named "UniqueColumn" exists, and its Unique property is true.
    myUniqueConstraint = New UniqueConstraint ( myTable.Columns ( "UniqueColumn" ) )
    myTable.Constraints.Add ( myUniqueConstraint )
End Sub