How will you remove duplicates in SQL?

Question

Accepted Answer

To delete duplicate records in SQL, use the DELETE statement with a subquery to identify and remove the duplicates.

Use the GROUP BY clause to group the records by the columns that define duplicates.
Use the HAVING clause to filter the groups and keep only the duplicates.
Use the DELETE statement with a subquery to delete the duplicate records.

Accepted Answer

Identify the duplicate records using the GROUP BY clause and the HAVING clause. For example:
SELECT column1, column2, COUNT() FROM table_name GROUP BY column1, column2 HAVING COUNT() > 1;
This will display all the rows where column1 and column2 have duplicate values.
Once you have identified the duplicate records, you can use the DELETE statement with a subquery to delete the duplicate rows. For example:
DELETE FROM table_name WHERE (column1, column2) IN (SELECT column1, column2 FROM table_name GROUP BY column1, column2 HAVING COUNT(*) > 1);
This will delete all the duplicate rows where column1 and column2 have the same values.

Note that before deleting any records, it's important to take a backup of the table or to test the DELETE statement on a subset of data to ensure that it does not delete any necessary information.

Accepted Answer

By deleting the rows which have count more than once

Asked in Indegene and 9 others

How will you remove duplicates in SQL?

Interview Questions from Popular Companies