Why Can\'t I Add a Foreign Key Constraint (Error Code 1215)?

Understanding Error Code 1215: "Cannot add foreign key constraint (foreign keys)" and its Alternatives

When establishing relationships between tables using foreign keys, it's crucial to ensure data consistency. However, you may encounter Error Code 1215: "Cannot add foreign key constraint (foreign keys)" during database creation. This error often arises when the data types of the referencing and referenced columns do not align.

In your specific case, the classLeader column in the class table has a VARCHAR(255) data type, while the referenced studentID column in the student table is likely an INT. To resolve this error, ensure that the data types of the two columns match.

Regarding your questions:

When filling tables with foreign keys:

Yes, you cannot directly fill the column designated for foreign keys. Instead, you must first insert data into the referenced table and then fill the foreign key column with the corresponding ID of the inserted record.

Foreign keys as keys:

Foreign keys are essential for maintaining data integrity. However, unlike primary keys, they are not unique identifiers for rows within a table. Instead, they establish relationships between rows from different tables. Primary keys ensure that each row in a table is distinct, while foreign keys guarantee that rows in one table correspond to existing rows in another table.

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