How to Remove Duplicate Records from a MySQL Table Efficiently Without Using Temporary Tables?

How to Delete Duplicate Records from a MySQL Table without Temporary Tables

In the context of data integrity, dealing with duplicate records can be a perplexing task. Consider a scenario where a table, TableA, contains multiple identical entries due to accidental double submissions. The challenge arises when you need to purge these duplicates while preserving at least one unique row.

UNIQUE INDEX Approach:

One effective method is to add a unique index on the relevant columns:

ALTER IGNORE TABLE `TableA`
ADD UNIQUE INDEX (`member_id`, `quiz_num`, `question_num`, `answer_num`);

This index enforces uniqueness on the specified columns, ensuring that no duplicate combinations can exist. As a result, attempts to insert identical records will be rejected by the database.

Primary Key Approach:

Alternatively, you can introduce a primary key in the table. A primary key is a unique identifier that distinguishes each row. By adding it to your existing table structure, you can subsequently execute:

DELETE FROM member
WHERE id IN (SELECT *
             FROM (SELECT id FROM member
                   GROUP BY member_id, quiz_num, question_num, answer_num HAVING (COUNT(*) > 1)
                  ) AS A
            );

This query identifies and removes duplicate rows by comparing their group counts and targeting rows with a count greater than 1. The id column can represent either your existing primary key or a new one added solely for this purpose.

Both approaches provide efficient solutions to the problem of duplicate records in your MySQL table, allowing you to maintain data integrity without the need for temporary tables.

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