Addressing MySQL Error 1022 (ER_DUP_KEY): Identifying and Resolving Duplicate Key Issues

Encountering Error 1022 in MySQL can halt your database operations. This error indicates that an attempt to insert or update a record has resulted in a violation of a unique constraint, trying to insert a duplicate key into a table. The error message typically reads:

Error 1022 - SQLSTATE: 23000 (ER_DUP_KEY) Can't write; duplicate key in table '%s'

Here %s is a placeholder for the table name. To resolve this error, you need to identify the cause of the duplicate key and take appropriate action. Below are steps to diagnose and fix this error:

Check Unique Constraints and Indexes

Ensure that the data you are trying to insert or update does not violate any unique constraints.

If you are inserting a new user into a users table with a unique email column, trying to insert a record with an email that already exists will cause Error 1022.

Sample Code:

INSERT INTO users (email, name) VALUES ('', 'John Doe');

To resolve this, ensure that the email being inserted is unique.

Review Your Insert or Update Queries

Make sure that the data in your INSERT or UPDATE queries does not conflict with existing unique keys.

When updating a user’s email to one that already exists in the database, you will encounter this error.

Sample Code:

UPDATE users SET email = '' WHERE id = 2;

To fix this, you can check for the existence of the email before attempting the update.


If your logic allows, use ON DUPLICATE KEY UPDATE to update the record if it already exists.

If inserting a record that might already exist and you want to update it instead, this clause can be used.

Sample Code:

INSERT INTO users (id, email, name) VALUES (1, '', 'John Doe')

This will update the name field if a duplicate key is found for the id.

Analyzing the Error Code

Look at the error code provided to understand which key is causing the problem. The error message should specify the key name.

The error might be Can't write; duplicate key in table 'users', key 'email_idx'. This tells you that the email_idx index is the one with the duplicate key issue.

Sample Code:
To investigate the index, you might use the following SQL command to show indexes from the table:


Database Cleanup

If the error is due to incorrect data, you may need to clean up the existing data in the table.

There might be data that was incorrectly inserted without proper unique constraints that now need to be cleaned up.

Sample Code:

DELETE FROM users WHERE email = '';

Before running such a command, ensure that you are only deleting the intended records.

By following these steps, you should be able to diagnose and correct the cause of MySQL Error 1022. Always make sure to have a backup of your database before making changes that could affect your data. If you are still experiencing issues after these steps, you may need to consult with a database administrator for further assistance.

Leave a Comment