Following code is useful to delete duplicate records. The table must have identity column, which will be used to identify the duplicate records. Table in example is has ID as Identity Column and Columns which have duplicate data are DuplicateColumn1, DuplicateColumn2 and DuplicateColumn3.
WHERE ID NOT IN
GROUP BY DuplicateColumn1, DuplicateColumn2, DuplicateColumn3)
Watch the view to see the above concept in action:
Reference : Pinal Dave (http://blog.SQLAuthority.com)