well, not exactly "use" -- you can define them but they are ignored
Originally Posted by da manual
InnoDB tables support checking of foreign key constraints. See Section 13.6, “The InnoDB Storage Engine”. Note that the FOREIGN KEY syntax in InnoDB is more restrictive than the syntax presented for the CREATE TABLE statement at the beginning of this section: The columns of the referenced table must always be explicitly named. InnoDB supports both ON DELETE and ON UPDATE actions on foreign keys. For the precise syntax, see Section 126.96.36.199, “FOREIGN KEY Constraints”.
For other storage engines, MySQL Server parses and ignores the FOREIGN KEY and REFERENCES syntax in CREATE TABLE statements.