How to Eliminate Duplicate Records in a MySQL Database with a Unique Key Constraint?

Purging Duplicate Records from a MySQL Database: A Unique Key Solution

Maintaining data integrity is crucial for the efficient operation of any database. In this instance, you encounter a table with an 'id' and 'title' column, where 'title' should be distinct. However, the presence of over 600,000 records, including numerous duplicates, poses a challenge in achieving uniqueness. Our goal is to eliminate these duplicate entries without compromising any unique titles.

The solution lies in utilizing the power of a unique key constraint. By adding a UNIQUE key to the 'title' column, we can effectively enforce uniqueness and prevent duplicate records from being inserted or updated. However, directly adding a unique key to a column with existing duplicates will result in errors.

To address this issue, we employ the 'ALTER IGNORE TABLE' command followed by the 'ADD UNIQUE KEY' clause. This command instructs MySQL to ignore errors that may arise during the addition of the unique key. As a result, all duplicate rows that would have violated the unique constraint are silently dropped, effectively eliminating the duplicates.

Here's the command syntax you can use:

<code class="sql">ALTER IGNORE TABLE table ADD UNIQUE KEY idx1(title);</code>

Note that this command may not be compatible with InnoDB tables in certain MySQL versions. For such cases, refer to this post for an alternative workaround.

By executing this command, you establish a unique key for the 'title' column and remove all duplicate records in one fell swoop. This allows you to maintain data integrity while ensuring the uniqueness of titles.

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