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。

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.

Oracle announced the general availability of MySQL Cluster 7.3, which adds foreign key support, a new NoSQL JavaScript Connector for node.js, and an auto-installer to make setting up clusters easier.