SELECT user,host FROM mysql.user;

SELECT USER(),CURRENT_USER();

DELETE FROM mysql.user WHERE user like '%';

SELECT user,host FROM mysql.user;

FLUSH PRIVILEGES;  

SELECT USER(),CURRENT_USER();

# Following query will produce ERROR 1449 on 10.4.14 and 10.5.4 (opt+dbg on both), 

# And "OK" on 10.1.46, 10.2.33, and 10.3.24 (dbg+opt both tested on all) and MySQL 5.5.62, 5.6.47, 5.7.29, and 8.0.19 (opt tested on all)

SELECT * FROM mysql.user;  

10.5.4>SELECT * FROM mysql.user;  

ERROR 1449 (HY000): The user specified as a definer ('mariadb.sys'@'localhost') does not exist