InnoDB also supports foreign key constraints. The syntax for a foreign
key constraint definition in InnoDB looks like this:

[CONSTRAINT symbol] FOREIGN KEY [id] (index_col_name, ...)
    REFERENCES tbl_name (index_col_name, ...)
    [ON DELETE {RESTRICT | CASCADE | SET NULL | NO ACTION}]
    [ON UPDATE {RESTRICT | CASCADE | SET NULL | NO ACTION}]

URL: http://dev.mysql.com/doc/refman/5.0/en/innodb-foreign-key-constraints.html

