create database test;

use test;

MariaDB [test]> select @@sql_mode;

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

| @@sql_mode |

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

|            |

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

1 row in set (0.000 sec)

MariaDB [test]> select @@global.sql_mode;

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

| @@global.sql_mode |

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

|                   |

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

1 row in set (0.000 sec)

/**/

create table article (id int unsigned not null auto_increment primary key, size bigint unsigned default 0);

insert into article values(NULL, 10);

DELIMITER $$

SET sql_mode = 'NO_UNSIGNED_SUBTRACTION';

CREATE TRIGGER article_update_quota BEFORE UPDATE ON `article`

FOR EACH ROW

BEGIN

  DECLARE _size_diff BIGINT DEFAULT 0;

  IF OLD.size != NEW.size THEN

    *SET _size_diff = NEW.size - OLD.size;*

  END IF;

END;

SET sql_mode = @@global.sql_mode;

$$

DELIMITER ;

update article set size=9; // FAILS with "BIGINT value is out of range in 'NEW.size - OLD.size'" altough trigger sql_mode: NO_UNSIGNED_SUBTRACTION