MariaDB [test]> create or replace table t (b blob, unique(b)) engine=InnoDB;

Query OK, 0 rows affected (0.057 sec)

MariaDB [test]> show create table t;

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

| Table | Create Table                                                                                                                                        |

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

| t     | CREATE TABLE `t` (

  `b` blob DEFAULT NULL,

  UNIQUE KEY `b` (`b`) USING HASH

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_uca1400_ai_ci |

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

1 row in set (0.001 sec)

MariaDB [test]> show index in t;

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

| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Ignored |

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

| t     |          0 | b        |            1 | b           | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               | NO      |

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

1 row in set (0.001 sec)