How Can I Find and Retrieve Duplicate Records in a MySQL Database?

Uncovering Duplicate Database Records in MySQL

In data management, identifying and handling duplicate records is crucial to ensure data integrity. MySQL offers a powerful way to retrieve duplicate records within a database using the GROUP BY and HAVING clauses.

The user's initial query demonstrates the ability to count duplicate addresses. However, the desired solution aims to retrieve the actual duplicate rows. To achieve this, the query can be modified to function as a subquery:

SELECT firstname, lastname, list.address
FROM list
INNER JOIN (SELECT address
FROM list
GROUP BY address
HAVING COUNT(id) > 1) dup
ON list.address = dup.address;

In this revised query, a subquery is created to retrieve the duplicate addresses. Subsequently, the main query joins the main list table with the subquery using the INNER JOIN condition list.address = dup.address. As a result, the query retrieves all rows from the list table associated with duplicate addresses, providing the desired output of each duplicate row.

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