Error
Error Code:
1823
MySQL Error 1823: Foreign Key System Table Constraint Failure
Description
MySQL Error 1823 indicates that the database system was unable to successfully add a foreign key constraint to its internal system tables. This typically occurs during `CREATE TABLE` or `ALTER TABLE` operations when defining or modifying foreign key relationships.
Error Message
Failed to add the foreign key constraint '%s' to system tables
Known Causes
4 known causesInsufficient User Permissions
The database user attempting to add the foreign key constraint lacks the necessary privileges to modify system tables or perform DDL operations on them.
Database Corruption or Internal Inconsistency
Underlying corruption within MySQL's data dictionary or system tables (e.g., `InnoDB` system tables) prevents the foreign key metadata from being stored correctly.
Incorrect Server Configuration
Certain MySQL server configuration settings, such as `innodb_force_recovery`, might be enabled, preventing normal DDL operations on system tables.
Concurrent DDL Operations
Another conflicting DDL operation on related tables or system tables might be in progress, causing a race condition or lock contention.
Solutions
3 solutions available1. Verify System Table Integrity medium
Check for and repair any corruption in MySQL's internal system tables.
1
Stop the MySQL server.
2
Navigate to your MySQL data directory. The exact path depends on your OS and installation.
3
Locate the `mysql` database directory. Inside, you'll find files like `innodb_table_stats.ibd`, `innodb_index_stats.ibd`, etc. These are system tables for InnoDB.
4
Run `mysqlcheck` with the `--repair` option for the `mysql` database. This tool can fix corrupted tables.
mysqlcheck --repair --all-databases -u root -p5
If `mysqlcheck` doesn't resolve the issue, you might need to manually inspect and potentially rebuild system table data. This is an advanced step and requires caution. Consult MySQL documentation for specific versions.
6
Start the MySQL server.
7
Attempt to create the foreign key constraint again.
2. Rebuild System Tables from a Backup advanced
Restore the `mysql` database from a known good backup.
1
Ensure you have a recent, verified backup of your entire MySQL data directory, or at least the `mysql` system database.
2
Stop the MySQL server.
3
Navigate to your MySQL data directory.
4
Backup the current `mysql` database directory to a safe location (e.g., `mv mysql mysql_backup_$(date +%Y%m%d_%H%M%S)`).
5
Restore the `mysql` database directory from your backup.
6
Start the MySQL server.
7
Attempt to create the foreign key constraint again.
3. Check for Invalid Data in System Tables advanced
Inspect system tables for inconsistencies that might prevent constraint creation.
1
Connect to your MySQL server as a user with sufficient privileges (e.g., root).
mysql -u root -p2
Examine the `mysql.innodb_table_stats` and `mysql.innodb_index_stats` tables for any unusual or invalid data. These tables store statistics for InnoDB tables and can sometimes become corrupted or contain inconsistent entries.
USE mysql;
SELECT * FROM innodb_table_stats WHERE last_update IS NULL OR last_update < '1970-01-01';
SELECT * FROM innodb_index_stats WHERE last_update IS NULL OR last_update < '1970-01-01';
-- Also check for rows with unexpected values or formats.3
If you find problematic rows, consider carefully deleting or updating them. This is a risky operation. It's highly recommended to first take a backup of the `mysql` database.
-- Example: DELETE FROM innodb_table_stats WHERE ...;
-- Example: UPDATE innodb_table_stats SET ... WHERE ...;4
If you're unsure about how to correct the data, consider the 'Rebuild System Tables from a Backup' solution.
5
After making any corrections, attempt to create the foreign key constraint.