Delete duplicate records

The following are the ways to delete duplicate rows from a table, and its purely depends upon your environment, its recommend to first try it on development server and then move ahead to production environment.

1. Using group by clause and move the records to another table, truncate original and move records back to original.

-- Create a table
CREATE TABLE t1 (
	col1 INT
	,col2 INT
	,col3 CHAR(50)
	)

--Insert some duplicate records
INSERT INTO t1 VALUES (1,1,'Manish')
INSERT INTO t1 VALUES (1,1,'Manish')
INSERT INTO t1 VALUES (1,2,'Sql server')

--Verify the records
SELECT * FROM t1

--Fetch and save the duplicate records into temporary table
SELECT *
INTO t2
FROM t1
GROUP BY col1
	,col2
	,col3
HAVING COUNT(*) > 1

SELECT * FROM t2

--Delete duplicate records from original table
DELETE
FROM t1
FROM t1
	,t2
WHERE t1.col1 = t2.col1
	AND t1.col2 = t2.col2
	AND t1.col3 = t2.col3

--Insert the delete data back
INSERT INTO t1 SELECT * FROM t2

--Verify
SELECT * FROM t1

--Cleanup
DROP TABLE t1
DROP TABLE t2

There are still more ways to delete duplicate records, will update this post some times later.
Thanks
Manish