MySQL 5.6 이하

SET PASSWORD FOR 'root'@'localhost' = PASSWORD('패스워드');

FLUSH PRIVILEGES;

MySQL 5.7 이하

UPDATE mysql.user SET password=PASSWORD('패스워드') WHERE user='root' AND Host='localhost';
FLUSH PRIVILEGES;

MySQL 5.7 이상

UPDATE mysql.user SET authentication_string=PASSWORD('패스워드') WHERE user='root' AND Host='localhost';
FLUSH PRIVILEGES;

MySQL 5.7.6 이상

ALTER USER 'root'@'localhost' IDENTIFIED BY '패스워드';

FLUSH PRIVILEGES;

MySQL 8.0 이상

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY '패스워드';

FLUSH PRIVILEGES;