MySQLではデータベースの一貫性を保つため、外部キー（Foreign Key）制約がサポートされています。

For Higher Computing Science, revise the use of primary and foreign keys and the difference between flat file and relational databases.

Can you do a foreign key within a single table, though? I've only ever seen foreign key constraints tying a field in one table to a field in another table.

Duplicate and Ignore on MySQL Inserts. MySQL table primary keys and unique indexes prevent multiple rows with the same index from being added to the table. If you try to insert a duplicate row ...