Wrong statement about VIRTUAL columns and indexes in KB article

If an index is defined on a PERSISTENT column then the optimizer considers using it in the same way as indexes based on "real" columns. VIRTUAL columns cannot be indexed.

[openxs@fc23 maria10.2]$ bin/mysql -uroot --socket=/tmp/mariadb.sock test

Reading table information for completion of table and column names

You can turn off this feature to get a quicker startup with -A

Welcome to the MariaDB monitor.  Commands end with ; or \g.

Your MariaDB connection id is 8

Server version: 10.2.17-MariaDB Source distribution

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [test]> create table tv(id int primary key, c1 varchar(10), c2 varchar(10) as (upper(c1)) virtual);

Query OK, 0 rows affected (0.15 sec)

MariaDB [test]> insert into tv(id, c1) values (1, 'abc');

Query OK, 1 row affected (0.04 sec)

MariaDB [test]> select * from tv;

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

| id | c1   | c2   |

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

|  1 | abc  | ABC  |

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

1 row in set (0.00 sec)

MariaDB [test]> alter table tv add key(c2);

Query OK, 0 rows affected (0.27 sec)

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [test]> show create table tv\G

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

       Table: tv

Create Table: CREATE TABLE `tv` (

  `id` int(11) NOT NULL,

  `c1` varchar(10) DEFAULT NULL,

  `c2` varchar(10) GENERATED ALWAYS AS (ucase(`c1`)) VIRTUAL,

  PRIMARY KEY (`id`),

  KEY `c2` (`c2`)

) ENGINE=InnoDB DEFAULT CHARSET=latin1

1 row in set (0.00 sec)

MariaDB [test]> explain select c2 from tv where c2 = 'ABC';

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

| id   | select_type | table | type | possible_keys | key  | key_len | ref   | rows | Extra                    |

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

|    1 | SIMPLE      | tv    | ref  | c2            | c2   | 13      | const |    1 | Using where; Using index |

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

1 row in set (0.00 sec)