Error
Error Code:
1557
MySQL Error 1557: Foreign Key Duplicate Entry
Description
This error occurs when attempting to create or enforce a foreign key constraint that would result in duplicate values within an index related to the foreign key in the child table. It typically signifies that existing data in the child table's foreign key column(s) violates a uniqueness requirement that the foreign key constraint, or an associated index, implicitly or explicitly demands.
Error Message
Upholding foreign key constraints for table '%s', entry '%s', key %d would lead to a duplicate entry
Known Causes
3 known causesDuplicate Child Foreign Key Values
The column(s) designated as the foreign key in the child table already contain duplicate entries, and the foreign key constraint or a related unique index requires these values to be unique.
Conflicting Unique Index
A unique index or primary key exists on the foreign key column(s) in the child table, and existing data violates this uniqueness when the foreign key is being added or enforced.
Incorrect Data Migration/Import
Data imported into the child table might contain duplicate values in the foreign key column, preventing the foreign key constraint from being successfully applied or validated.
Solutions
Coming SoonDetailed step-by-step solutions for this error are being prepared. In the meantime, try these general troubleshooting tips:
General Troubleshooting Tips
- Check the error message carefully for specific details
- Review recent changes that might have caused the error
- Search for the exact error code in the official documentation
- Check log files for additional context
- Try restarting the application or service