mysql> create table n1 (uq int auto_increment primary key,
    -> fld1 int,
    -> index (fld1)) type=innodb;
Query OK,  0  rows affected ( 0 . 15  sec)

mysql> insert into n1 (fld1) values ( 1 ),( 2 ),( 3 );
Query OK,  3  rows affected ( 0 . 05  sec)
Records:  3   Duplicates:  0   Warnings:  0 

mysql> create table n3 (i int,
    -> index (i),
    -> foreign key (i) references n1(fld1) on delete cascade) type=innodb;
Query OK,  0  rows affected ( 0 . 03  sec)

mysql> insert into n3 values( 1 ),( 1 ),( 2 ),( 2 );
Query OK,  4  rows affected ( 0 . 00  sec)
Records:  4   Duplicates:  0   Warnings:  0 

mysql> insert into n3 values( 100 );
ERROR  1216 : Cannot add or update a child row: a foreign key constraint fails

mysql> select * from n1;
+ ----+------+
 
| uq | fld1 |
+ ----+------+
 
|   1  |     1  |
|   2  |     2  |
|   3  |     3  |
+ ----+------+
 
 3  rows in set ( 0 . 03  sec)

mysql> select * from n3;
+ ------+
 
| i    |
+ ------+
 
|     1  |
|     1  |
|     2  |
|     2  |
+ ------+
 
 4  rows in set ( 0 . 00  sec)

mysql> delete from n1 where fld1 =  1 ;
Query OK,  1  row affected ( 0 . 05  sec)

mysql> select * from n3;
+ ------+
 
| i    |
+ ------+
 
|     2  |
|     2  |
+ ------+
 
 2  rows in set ( 0 . 00  sec)

mysql> select version();
+ -----------+
 
| version() |
+ -----------+
 
|  4 . 0 . 14     |
+ -----------+
 
 1  row in set ( 0 . 02  sec)