How to delete duplicate rows in SQL Server?

I like CTEs and ROW_NUMBER as the two combined allow us to see which rows are deleted (or updated), therefore just change the DELETE FROM CTE... to SELECT * FROM CTE:

WITH CTE AS(   SELECT [col1], [col2], [col3], [col4], [col5], [col6], [col7],       RN = ROW_NUMBER()OVER(PARTITION BY col1 ORDER BY col1)   FROM dbo.Table1)DELETE FROM CTE WHERE RN > 1

DEMO (result is different; I assume that it's due to a typo on your part)

COL1    COL2    COL3    COL4    COL5    COL6    COL7john    1        1       1       1       1       1sally   2        2       2       2       2       2

This example determines duplicates by a single column col1 because of the PARTITION BY col1. If you want to include multiple columns simply add them to the PARTITION BY:

ROW_NUMBER()OVER(PARTITION BY Col1, Col2, ... ORDER BY OrderColumn)

I would prefer CTE for deleting duplicate rows from sql server table

strongly recommend to follow this article ::http://codaffection.com/sql-server-article/delete-duplicate-rows-in-sql-server/

by keeping original

WITH CTE AS(SELECT *,ROW_NUMBER() OVER (PARTITION BY col1,col2,col3 ORDER BY col1,col2,col3) AS RNFROM MyTable)DELETE FROM CTE WHERE RN<>1

without keeping original

WITH CTE AS(SELECT *,R=RANK() OVER (ORDER BY col1,col2,col3)FROM MyTable) DELETE CTEWHERE R IN (SELECT R FROM CTE GROUP BY R HAVING COUNT(*)>1)

Without using CTE and ROW_NUMBER() you can just delete the records just by using group by with MAX function here is and example

DELETEFROM MyDuplicateTableWHERE ID NOT IN(SELECT MAX(ID)FROM MyDuplicateTableGROUP BY DuplicateColumn1, DuplicateColumn2, DuplicateColumn3)