Error
Error Code:
1391
MySQL Error 1391: Zero-Length Key Part
Description
MySQL Error 1391 occurs when a key part (a column used in an index or foreign key) is defined with a length of zero, which is not permitted. This typically happens during schema modifications like creating tables, altering tables, or adding indexes, preventing the operation from completing.
Error Message
Key part '%s' length cannot be 0
Known Causes
3 known causesExplicit Zero-Length Key Definition
The SQL statement explicitly defines a key part (e.g., for a PRIMARY KEY, UNIQUE KEY, or INDEX) with a length of 0.
Missing Length for TEXT/BLOB Index
An index is being created on a TEXT or BLOB column without specifying a required length prefix, implicitly resulting in a zero length for the key part.
Foreign Key Length Mismatch
A foreign key constraint definition involves a column where the key part implicitly resolves to an invalid zero length, often due to an incompatible or malformed column definition.
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