MariaDB vs MySQL: default expression in column definition not working

I am using a table in MySQL to store and calculate time differences when generating materialized views.

CREATE TABLE `creationtime` (
	`view` VARCHAR(255) NULL DEFAULT NULL COLLATE 'utf8mb4_general_ci',
	`start` DATETIME NULL DEFAULT NULL,
	`stop` DATETIME NULL DEFAULT NULL,
	`diff` TIME NOT NULL DEFAULT timediff(`stop`,`start`)
)
COMMENT='running time'
COLLATE='utf8mb4_general_ci'
ENGINE=InnoDB
;

This works perfectly: Start and stop time values are stored and when I open the table the time differences are calculated on the fly.

Now I wanted to use the same syntax on a MariaDB-Server (MariaDB version 10.1.48 on Debian Linux 9). But I am running into an error.

> /* SQL-Error (1064): You have an error in your SQL syntax; check the
> manual that corresponds to your MariaDB server version for the right
> syntax to use near 'timediff(`stop`,`start`) ) COMMENT='running time'
> COLLATE='utf8mb4_general_ci' at line 5 */

I don't get it. Where is the error?

https://mariadb.com/kb/en/create-table/#default-column-option says:

> The DEFAULT clause was enhanced in MariaDB 10.2.1. Some enhancements include:
>
> - The DEFAULT clause can now be used with an expression or function.

Since you are currently using MariaDB 10.1, you need to upgrade to get this feature. Since MariaDB 10.1 passed its end of support in October 2020, you should have upgraded long ago. Version 10.2 is also EOL, and 10.3 is almost at its end of support (next month, May 2023).

Make sure you read the knowledgebase page I linked to above for examples of the DEFAULT syntax. There are subtle differences from the syntax for expression defaults in MySQL.