MariaDB [test]> create or replace table t (a vector(1) not null, key(a)) engine=InnoDB;

Query OK, 0 rows affected (0.094 sec)

MariaDB [test]> create table t2 (b vector(1) not null, vector(b), foreign key(b) references t(a)) engine=InnoDB;

ERROR 1005 (HY000): Can't create table `test`.`t2` (errno: 150 "Foreign key constraint is incorrectly formed")

MariaDB [test]> show warnings;

+---------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+

| Level   | Code | Message                                                                                                                                                               |

+---------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+

| Warning |  150 | Create  table `test`.`t2` with foreign key (b) constraint failed. There is no index in the referenced table where the referenced columns appear as the first columns. |

| Error   | 1005 | Can't create table `test`.`t2` (errno: 150 "Foreign key constraint is incorrectly formed")                                                                            |

| Warning | 1215 | Cannot add foreign key constraint for `t2`                                                                                                                            |

+---------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+

3 rows in set (0.000 sec)

MariaDB [test]> create or replace table t2 (b vector(1) not null, foreign key(b) references t(a)) engine=InnoDB;

Query OK, 0 rows affected (0.078 sec)

MariaDB [test]> show create table t2\G

*************************** 1. row ***************************

       Table: t2

Create Table: CREATE TABLE `t2` (

  `b` vector(1) NOT NULL,

  KEY `b` (`b`),

  CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`b`) REFERENCES `t` (`a`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_uca1400_ai_ci

1 row in set (0.001 sec)

MariaDB [test]> create or replace table t2 (b vector(1) not null, vector(b), key(b), foreign key(b) references t(a)) engine=InnoDB;

Query OK, 0 rows affected (0.167 sec)

MariaDB [test]> show create table t2\G

*************************** 1. row ***************************

       Table: t2

Create Table: CREATE TABLE `t2` (

  `b` vector(1) NOT NULL,

  KEY `b_2` (`b`),

  VECTOR KEY `b` (`b`),

  CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`b`) REFERENCES `t` (`a`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_uca1400_ai_ci