_set_client system
variable when the trigger was created. 
* collation_connection is the session value of the collation_connection system
variable when the trigger was
 created. 
* Database Collation is the collation of the database 
 with which the trigger is associated.

These columns were added in MariaDB/MySQL 5.1.21.

Old triggers created before MySQL 5.7 and MariaDB 10.2.3 has NULL in the
Created column.

URL: https://mariadb.com/kb/en/show-triggers/https://mariadb.com/kb/en/show-triggers/