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.

There are so many problems with foreign key constraints that we don't know where to start: Foreign key constraints make life very complicated, because the foreign key definitions must be stored in a ...

Indexes in MySQL are used to speed up access in the database and help enforce database constraints (such as UNIQUE and FOREIGN KEY). Database indexes are much like book indexes.