MariaDB [test]> CREATE TABLE t5 (c1 INT) ENGINE = XtraDB;

Query OK, 0 rows affected, 2 warnings (0.08 sec)

MariaDB [test]> ALTER TABLE t5 ADD INDEX i1 (c1) USING hash;

Query OK, 0 rows affected (0.14 sec)

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [test]> SHOW WARNINGS;

Empty set (0.00 sec)

MariaDB [test]> SHOW INDEX FROM t5;

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

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

| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardi

nality | Sub_part | Packed | Null | Index_type | Comment |

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

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

| t5    |          1 | i1       |            1 | c1          | A         |

  NULL |     NULL | NULL   | YES  | BTREE      |         |

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

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

1 row in set (0.00 sec)

MariaDB [test]>