Why Does ALTER IGNORE TABLE Still Throw a 'Duplicate Entry' Error in MySQL?

MySQL: ALTER IGNORE TABLE Raises "Integrity Constraint Violation" Despite Documentation

The MySQL documentation clearly states that using ALTER IGNORE TABLE, when combined with a UNIQUE KEY, should allow for the removal of duplicates by overriding any duplicate-key errors. However, in practice, users have encountered the persistent error message "#1062 - Duplicate entry 'blabla' for key 'dupidx'".

This behavior appears to be caused by a bug in the InnoDB version of MySQL on certain versions. Specifically, the IGNORE keyword extension does not function as expected in the InnoDB context.

Solution:

To circumvent this issue, users can employ the following workaround:

1. Convert the table to MyISAM using: ALTER TABLE table ENGINE MyISAM;
2. Apply the ALTER IGNORE TABLE command with the UNIQUE INDEX: ALTER IGNORE TABLE table ADD UNIQUE INDEX dupidx (field);
3. Convert the table back to InnoDB using: ALTER TABLE table ENGINE InnoDB;

Note: If the table contains Foreign Key constraints, removing and re-adding them will be necessary to ensure data integrity.

The above is the detailed content of Why Does ALTER IGNORE TABLE Still Throw a 'Duplicate Entry' Error in MySQL?. For more information, please follow other related articles on the PHP Chinese website!