引用元 : MySQL8.0ではGRANT構文でユーザを作成できない – guro_chanの手帳

grant all on *.* to 'guro'@'localhost' identified by 'avava' with grant option;

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create user 'guro'@'localhost' identified by 'avava';
grant all on *.* to 'guro'@'localhost' with grant option;
flush privileges;