Syntax:
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 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.

As of MySQL 5.7.8, the IF EXISTS clause can be used, which causes the
statement to produce a warning for each named account that does not
exist, rather than an error.

Each account name uses the format described in
http://dev.mysql.com/doc/refman/5.7/en/account-names.html. For example:

DROP USER 'jeffrey'@'localhost';

The host name part of the account name, if omitted, defaults to '%'.

URL: http://dev.mysql.com/doc/refman/5.7/en/drop-user.html

