% mysql test
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 183
Server version: 5.1.41-3ubuntu12.6 (Ubuntu)

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> \W
Show warnings enabled.
mysql> create table foo(foo_id int primary key) engine=InnoDB;
Query OK, 0 rows affected (0.00 sec)

mysql> create table bar(
    ->     foo_id int references foo (foo_id)
    -> ) engine=InnoDB;
Query OK, 0 rows affected (0.01 sec)

mysql> show create table bar\G
*************************** 1. row ***************************
       Table: bar
Create Table: CREATE TABLE `bar` (
  `foo_id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)

/* ^ Notice the glaring lack of foreign key constraint?!?
 * No errors, no warnings, no constraint.
 *
 * http://dev.mysql.com/doc/refman/5.1/en/innodb-foreign-key-constraints.html
 *
 * "Furthermore, InnoDB does not recognize or support “inline REFERENCES
 * specifications” (as defined in the SQL standard) where the references are defined
 * as part of the column specification. InnoDB accepts REFERENCES clauses only when
 * specified as part of a separate FOREIGN KEY  specification."
 */