语句如下：

create_user_stmt:
    CREATE USER [IF NOT EXISTS] user_name [IDENTIFIED BY 'password'];
alter_user_stmt:
      ALTER USER user_name ACCOUNT {LOCK | UNLOCK};
    | ALTER USER user_name IDENTIFIED BY 'password';
    | SET PASSWORD [FOR user_name] = PASSWORD('password');
    | RENAME USER rename_user_action_list;
drop_user_stmt:
    DROP USER user_name_list;
rename_user_action_list:
    rename_user_action [, rename_user_action ...]
rename_user_action:
    user_name TO user_name
user_name_list:
    user_name [, user_name ...]
password:
    STR_VALUE

create_user_stmt:
    CREATE USER [IF NOT EXISTS] user_name [IDENTIFIED BY 'password'];
alter_user_stmt:
      ALTER USER user_name ACCOUNT {LOCK | UNLOCK};
    | ALTER USER user_name IDENTIFIED BY 'password';
    | SET PASSWORD [FOR user_name] = PASSWORD('password');
    | RENAME USER rename_user_action_list;
drop_user_stmt:
    DROP USER user_name_list;
rename_user_action_list:
    rename_user_action [, rename_user_action ...]
rename_user_action:
    user_name TO user_name
user_name_list:
    user_name [, user_name ...]
password:
    STR_VALUE