Find duplicates in a table and delete them using SQL Server 2005

It is a very common requirement to find duplicates in table based on a column or set of columns and then delete them. Let us see how to do that:

Sample Table

DROP TABLE #Customers
GO

CREATE TABLE #Customers (CustID int, CustName varchar(10), PostalCode int)
INSERT #Customers SELECT 1,'A',100
INSERT #Customers SELECT 1,'B',100
INSERT #Customers SELECT 2,'C',100
INSERT #Customers SELECT 3,'D',100
INSERT #Customers SELECT 4,'E',100
INSERT #Customers SELECT 5,'F',100
INSERT #Customers SELECT 5,'G',100
INSERT #Customers SELECT 6,'H',200
INSERT #Customers SELECT 7,'I',300

Find Duplicates in CustID

SELECT CustID
FROM #Customers
GROUP BY CustID HAVING count(*) > 1

returns you the duplicate CustID

Delete Duplicates in the Customer table

SET ROWCOUNT 1
SELECT NULL
WHILE @@rowcount > 0
DELETE cust
FROM #Customers as cust
INNER JOIN
(SELECT CustID
FROM #Customers
GROUP BY CustID HAVING count(*) > 1)
AS c ON c.CustID = cust.CustID
SET ROWCOUNT 0

SELECT * FROM #Customers

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About The Author

Suprotim Agarwal, ASP.NET Architecture MVP works as an Architect Consultant and provides consultancy on how to design and develop Web applications.

Suprotim is also the founder and primary contributor to DevCurry, DotNetCurry and SQLServerCurry. He has also written an EBook 51 Recipes using jQuery with ASP.NET Controls.

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