CREATE TABLE `simple` (

  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,

  `modified` timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(),

  `val` int(10) unsigned DEFAULT NULL,

  `blah` varchar(511) DEFAULT NULL,

  PRIMARY KEY (`id`),

  KEY `simple_modified` (`modified`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

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

| Variable_name                        | Value       |

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

| innodb_stats_auto_recalc             | ON          |

| innodb_stats_include_delete_marked   | OFF         |

| innodb_stats_method                  | nulls_equal |

| innodb_stats_modified_counter        | 0           |

| innodb_stats_on_metadata             | OFF         |

| innodb_stats_persistent              | ON          |

| innodb_stats_persistent_sample_pages | 20          |

| innodb_stats_sample_pages            | 8           |

| innodb_stats_traditional             | ON          |

| innodb_stats_transient_sample_pages  | 8           |

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

MariaDB [test]> show index from simple;

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

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

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

| simple |          0 | PRIMARY         |            1 | id          | A         |       14391 |     NULL | NULL   |      | BTREE      |         |               |

| simple |          1 | simple_modified |            1 | modified    | A         |        2055 |     NULL | NULL   |      | BTREE      |         |               |

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

2 rows in set (0.000 sec)

MariaDB [test]> select count(*) from simple;

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

| count(*) |

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

|    14722 |

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

1 row in set (0.005 sec)

MariaDB [test]> select count(distinct modified) from simple;

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

| count(distinct modified) |

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

|                      362 |

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

1 row in set (0.001 sec)

MariaDB [test]> show index from simple;

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

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

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

| simple |          0 | PRIMARY         |            1 | id          | A         |       14383 |     NULL | NULL   |      | BTREE      |         |               |

| simple |          1 | simple_modified |            1 | modified    | A         |       14383 |     NULL | NULL   |      | BTREE      |         |               |

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

2 rows in set (0.000 sec)

MariaDB [test]> select count(*) from simple;

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

| count(*) |

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

|    14722 |

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

1 row in set (0.005 sec)

MariaDB [test]> select count(distinct modified) from simple;

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

| count(distinct modified) |

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

|                      362 |

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

1 row in set (0.001 sec)