Question

In data migration, there is often a need to delete duplicate rows as part of data cleanup. Which statement works best?

a) DELETE DUPLICATES
b) REMOVE DUPLICATES
c) DELETE IGNORE
d) DELETE WHERE DUPLICATE

Answer 1

The correct way to delete duplicate rows during data migration involves using standard SQL commands, which typically consist of a DELETE statement combined with a subquery to identify and remove duplicates. None of the options provided in the question are valid SQL syntax.

Step-by-step explanation:

When performing data migration and cleanup, neither of the statements 'DELETE DUPLICATES', 'REMOVE DUPLICATES', 'DELETE IGNORE', or 'DELETE WHERE DUPLICATE' are standard SQL commands for removing duplicate rows. Instead, a common approach involves using a combination of the DELETE statement with a subquery that identifies duplicates. For instance, in SQL, you might use a command that looks something like this:
DELETE FROM table_name WHERE row_id NOT IN (SELECT MIN(row_id) FROM table_name GROUP BY column_name HAVING COUNT(*) > 1);
This statement deletes all rows for which the ID is not the minimum ID in the group of duplicate rows, based on a specific column_name that you're using to determine duplicates. Remember that the specific SQL code can vary based on the database system you are using (MySQL, PostgreSQL, etc.), and always ensure you have a backup of your data before making such changes.