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Why Am I Getting MySQL Error Code 1215: Cannot Add Foreign Key Constraint?

Linda Hamilton

Nov 26, 2024 am 08:16 AM

Why Am I Getting MySQL Error Code 1215: Cannot Add Foreign Key Constraint?

Error Code 1215: Foreign Key Constraint and Data Consistency

When defining foreign key constraints to ensure data consistency between tables, certain requirements must be met. Error Code 1215, "Cannot add foreign key constraint (foreign keys)," occurs when these requirements are not fulfilled.

The error arises due to a datatype mismatch between the foreign key column and the referenced column. In this case, the foreign key column "classLeader" has a VARCHAR(255) datatype, while the referenced column "studentID" in the "student" table has an INT datatype. Foreign keys must have the same datatype as the referenced column.

Furthermore, the referenced table and column must exist. The "student" table should be created before attempting to define the foreign key constraint, and the "studentID" column should be the primary key or have a unique index.

Lastly, it's crucial to understand that foreign keys are not true keys. While they are used to enforce data integrity, they do not participate in indexing or uniqueness checks.

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