$ mysql -u root -p
Enter password:

mysql> use mysql;

Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

// mysql 5.x 는 "password" 또는 "authentication_string"로 확인합니다.
mysql> select host, user, password from user;
mysql> select host, user, authentication_string from user;

// mysql 8.x
mysql> select host, user, authentication_string from user;

// mysql 5.x
mysql> update user set password=password('1234') where user='root';
mysql> update user set authentication_string=password('1234') where user='root';

// mysql 8.x
mysql> alter user 'root'@'localhost' identified with mysql_native_password by '1234;

mysql> flush privileges;
mysql> quit
Bye