Deleting Duplicate Player Names

Oct 13, 2025 by wbrum.org 61 views

Introduction

When working with large datasets, it's not uncommon to encounter duplicate records. In this article, we'll explore how to delete duplicate player names from a SQL database while preserving records that are associated with games. We'll use the ROW_NUMBER() function to achieve this.

Table Structure

Let's assume we have two tables: Players and Games. The Players table contains information about individual players, while the Games table contains information about games played by these players.

Players Table

Column Name	Data Type	Description
PlayerID	int	Unique identifier for each player
Name	varchar(255)	Player's name
Age	int	Player's age

Games Table

Column Name	Data Type	Description
GameID	int	Unique identifier for each game
PlayerID	int	Foreign key referencing the PlayerID in the Players table
GameDate	date	Date the game was played

Deleting Duplicate Player Names

To delete duplicate player names, we'll use the ROW_NUMBER() function to assign a unique row number to each player based on their name. We'll then use this row number to identify and delete duplicate records.

WITH DuplicatePlayers AS (
  SELECT Name, ROW_NUMBER() OVER (PARTITION BY Name ORDER BY PlayerID) AS RowNum
  FROM Players
)
DELETE FROM DuplicatePlayers
WHERE RowNum > 1;

This query uses a Common Table Expression (CTE) to assign a unique row number to each player based on their name. The PARTITION BY clause groups players by their name, and the ORDER BY clause sorts players by their PlayerID. The ROW_NUMBER() function assigns a unique row number to each player, starting from 1.

The outer query then deletes all rows where the row number is greater than 1, effectively deleting all duplicate player names.

Preserving Records Associated with Games

However, this query will delete all duplicate player names, including those associated with games. To preserve these records, we need to modify the query to exclude players who have games associated with them.

WITH DuplicatePlayers AS (
  SELECT Name, ROW_NUMBER() OVER (PARTITION BY Name ORDER BY PlayerID) AS RowNum
  FROM Players
  WHERE PlayerID NOT IN (SELECT PlayerID FROM Games)
)
DELETE FROM DuplicatePlayers
WHERE RowNum > 1;

This modified query uses a subquery to exclude players who have games associated with them. The subquery selects all PlayerIDs from the Games table, and the outer query excludes these PlayerIDs from the Players table.

Example Use Case

Let's assume we have the following data in our Players and Games tables:

Players Table

PlayerID	Name	Age
1	John	25
2	Jane	30
3	John	25
4	Jane	30

Games Table

GameID	PlayerID	GameDate
1	1	2022-01-01
2	2	2022-01-02
3	3	2022-01-03

Running the modified query will delete the duplicate player names, leaving only one record for each player:

Players Table

PlayerID	Name	Age
1	John	25
2	Jane	30

The records associated with games will be preserved, as shown in the Games table:

Games Table

GameID	PlayerID	GameDate
1	1	2022-01-01
2	2	2022-01-02
3	3	2022-01-03

Conclusion

Q: What is the purpose of using the ROW_NUMBER() function in this query?

A: The ROW_NUMBER() function is used to assign a unique row number to each player based on their name. This allows us to identify and delete duplicate records.

Q: Why do we need to use a Common Table Expression (CTE) in this query?

A: A CTE is used to simplify the query and make it easier to read. It allows us to assign a temporary name to a result set, which can then be used in the outer query.

Q: How does the PARTITION BY clause work in this query?

A: The PARTITION BY clause groups players by their name, so that players with the same name are assigned the same row number.

Q: What is the purpose of the ORDER BY clause in this query?

A: The ORDER BY clause sorts players by their PlayerID, so that players with the same name are assigned a unique row number based on their PlayerID.

Q: Why do we need to use a subquery to exclude players who have games associated with them?

A: We need to use a subquery to exclude players who have games associated with them because we want to preserve these records. By excluding these players, we can ensure that the query only deletes duplicate player names that are not associated with games.

Q: Can this query be modified to delete duplicate player names based on other criteria, such as age or game date?

A: Yes, this query can be modified to delete duplicate player names based on other criteria. For example, we could modify the PARTITION BY clause to group players by their age or game date, and then assign a unique row number to each player based on this criteria.

Q: What are some potential issues that may arise when using this query?

A: Some potential issues that may arise when using this query include:

Deleting records that are associated with games, which may cause data inconsistencies.
Deleting records that are not duplicates, which may cause data loss.
Using the wrong criteria to identify duplicate records, which may cause incorrect results.

Q: How can we troubleshoot issues that arise when using this query?

A: To troubleshoot issues that arise when using this query, we can:

Check the query results to ensure that the correct records are being deleted.
Verify that the query is using the correct criteria to identify duplicate records.
Use debugging tools to identify any errors or issues with the query.

Q: Can this query be used in other scenarios, such as deleting duplicate records in other tables?

A: Yes, this query can be used in other scenarios, such as deleting duplicate records in other tables. We can modify the query to use the correct table and columns, and then use the same logic to delete duplicate records.

Q: What are some best practices for using this query?

A: Some best practices for using this query include:

Testing the query thoroughly before using it in production.
Verifying that the query is using the correct criteria to identify duplicate records.
Using debugging tools to identify any errors or issues with the query.
Documenting the query and its results to ensure that it can be easily understood and maintained.