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SQL Puzzle | Delete Duplicate Records using Outer Join
This puzzle is really simple. You have to write a query which will delete duplicate records from a table. The sample table we are using has a single column called Id. This was asked to me at a recent technical discussion.
Please check out the sample input and the expected output below-
- The solution should be should use “SELECT” statement or a CTE.
- Add your solution(s) in the comments section or send you solution(s) to firstname.lastname@example.org
Script | use below script to create table & insert some sample data
-- CREATE TABLE DeleteDuplicateUsingOuterJoin ( ID SMALLINT ) GO INSERT INTO DeleteDuplicateUsingOuterJoin VALUES (1), (2), (2), (3), (3), (3) GO --
Solution 1 | Left Outer Join
-- ;WITH CTE AS ( SELECT * , ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) rnk FROM DeleteDuplicateUsingOuterJoin ) DELETE p FROM CTE p LEFT OUTER JOIN ( SELECT MIN(rnk) ID FROM CTE GROUP BY ID )u ON u.ID = p.rnk WHERE u.ID IS NULL --
Also check out the other SQL Puzzles containing duplicates –
Add a comment if you have any other solution in mind. I would love to learn it. We all need to learn.
Enjoy !!! Keep Learning