Explanation:
Example:
let us write a query which will delete all duplicate data in one shot. We will use a CTE (Common Table Expression) for this purpose. We will read in future posts what a CTE is and why it is used. On a lighter note, CTE's can be imagined as equivalent to temporary result sets that can be used only in an underlying SELECT, INSERT, UPDATE, DELETE or CREATE VIEW statement.
;WITH CTE AS
(
SELECT Name
, City
, [State]
, ROW_NUMBER() OVER(PARTITION BY Name, City, [State] ORDER BY [Name]) AS Rnum FROM Persons ) DELETE FROM CTE WHERE Rnum <> 1 In the code by saying WHERE Rnum <> 1, we are asking SQL Server to keep all the records with Rank 1, which are not duplicates, and delete any other record. After executing this query in SQL Server Management Studio, you will end up with no duplicates in your table. To confirm that just run a simple query against your table.
Reference:
http://social.technet.microsoft.com/wiki/contents/articles/22706.how-to-remove-duplicates-from-a-table-in-sql-server.aspx