How to create functional index on mariadb?

Question

I'm trying to create functional index on mariadb 5.5 like below...

MariaDB [testdb]> create table foo(c1 datetime);
Query OK, 0 rows affected (0.43 sec)

MariaDB [testdb]> alter table foo add c2 varchar(10) AS (date_format(c1, '%Y-%m-%d')); 
Query OK, 0 rows affected (0.22 sec)               
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [testdb]> desc foo;
+-------+-------------+------+-----+---------+---------+
| Field | Type        | Null | Key | Default | Extra   |
+-------+-------------+------+-----+---------+---------+
| c1    | datetime    | YES  |     | NULL    |         |
| c2    | varchar(10) | YES  |     | NULL    | VIRTUAL |
+-------+-------------+------+-----+---------+---------+
2 rows in set (0.03 sec)

MariaDB [testdb]> create index idx_foo on foo(c1, c2);
ERROR 1904 (HY000): Key/Index cannot be defined on a non-stored computed column
MariaDB [testdb]> 

Is there any how to create compositional column based index with VIRUAL column?

Any advice would be appreciated.

Thanks in advance.

Answer 1

See documentation:

Generated (Virtual and Persistent/Stored) Columns

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MariaDB until 10.2.2

In MariaDB 10.2.2 and before, the following statements apply to indexes for generated columns:

• Defining indexes on VIRTUAL generated columns is not supported.
• ...

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