DROP USER [IF EXISTS] user [, user] ...
        The DROP USER statement removes
        one or more MySQL accounts and their privileges. It removes
        privilege rows for the account from all grant tables.
      
        To use DROP USER, you must have
        the global CREATE USER privilege,
        or the DELETE privilege for the
        mysql system database. When the
        read_only system variable is
        enabled, DROP USER additionally
        requires the SUPER privilege.
      
        An error occurs if you try to drop an account that does not
        exist. If the IF EXISTS clause is given, the
        statement produces a warning for each named user that does not
        exist, rather than an error.
      
Each account name uses the format described in Section 6.2.4, “Specifying Account Names”. For example:
DROP USER 'jeffrey'@'localhost';
        The host name part of the account name, if omitted, defaults to
        '%'.
          DROP USER does not
          automatically close any open user sessions. Rather, in the
          event that a user with an open session is dropped, the
          statement does not take effect until that user's session is
          closed. Once the session is closed, the user is dropped, and
          that user's next attempt to log in fails. This
          is by design.
        DROP USER does not automatically
        drop or invalidate databases or objects within them that the old
        user created. This includes stored programs or views for which
        the DEFINER attribute names the dropped user.
        Attempts to access such objects may produce an error if they
        execute in definer security context. (For information about
        security context, see
        Section 23.6, “Stored Object Access Control”.)