Error
Error Code:
1240
MySQL Error 1240: Foreign Key Mismatch
Description
Error 1240 occurs when defining a foreign key constraint where the referencing columns in the child table do not structurally match the referenced columns in the parent table. This typically happens during `CREATE TABLE` or `ALTER TABLE` statements when establishing relationships between tables.
Error Message
Key reference and table reference don't match
Known Causes
3 known causesColumn Count Mismatch
The number of columns specified in your foreign key definition does not match the number of columns in the primary or unique key it references in the parent table.
Data Type Inconsistency
The data types, lengths, or character sets of the foreign key columns do not align with those of the referenced columns in the parent table.
Referencing Invalid Parent Key
The foreign key attempts to reference columns in the parent table that are not part of a primary key or a unique key, which is a requirement for foreign key constraints.
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