How to delete duplicate rows in SQL Server

0 votes

How will I be able to delete the duplicate rows where no unique row id exists?

My table is

col1 col2 col3 col4 col5 col6 col7 
john 1 1 1 1 1 1 
john 1 1 1 1 1 1 
sally 2 2 2 2 2 2 
sally 2 2 2 2 2 2

I want to be left with the following after the duplicate removal:

john 1 1 1 1 1 1 
sally 2 2 2 2 2 2

I also tried a few queries but I think they depend on having a row id as I don't get the desired result. For example:

DELETE 
FROM table 
WHERE col1 IN ( 
          SELECT id 
          FROM table 
          GROUP BY id 
          HAVING (COUNT(col1) > 1)
)
Feb 10, 2022 in Others by Rahul
• 9,670 points
940 views

1 answer to this question.

0 votes

To answer your query, note that CTEs and ROW_NUMBER are the both combined, which allow us to see which rows are deleted and hence, just make the change to 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

The DEMO result is different and hence, I assume that it's due to a typo on your part.
 

COL1 COL2 COL3 COL4 COL5 COL6 COL7 
john 1 1 1 1 1 1 
sally 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)
answered Feb 10, 2022 by Soham
• 9,700 points

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