mysql> create table foo (id integer primary key, name varchar(10));
Query OK, 0 rows affected (0.01 sec)

mysql> create table boo (id integer primary key, foo_id integer references foo(id));
Query OK, 0 rows affected (0.00 sec)

mysql> create table bar (id integer primary key, foo_id integer, constraint foo_id_fk foreign key (foo_id) references foo(id));
Query OK, 0 rows affected (0.00 sec)

mysql> show create table boo;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                               |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------+
| boo   | CREATE TABLE `boo` (
  `id` int(11) NOT NULL,
  `foo_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show create table bar;
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                      |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| bar   | CREATE TABLE `bar` (
  `id` int(11) NOT NULL,
  `foo_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `foo_id_fk` (`foo_id`),
  CONSTRAINT `foo_id_fk` FOREIGN KEY (`foo_id`) REFERENCES `foo` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> drop table foo;
ERROR 1217 (23000): Cannot delete or update a parent row: a foreign key constraint fails
mysql> drop table bar;
Query OK, 0 rows affected (0.00 sec)

mysql> drop table foo;
Query OK, 0 rows affected (0.00 sec)