Syntax:
ALTER USER user_specification
    [, user_specification] ...

user_specification:
    user PASSWORD EXPIRE

The ALTER USER statement alters MySQL accounts. To use it, you must
have the global CREATE USER privilege or the INSERT privilege for the
mysql database. This statement was added in MySQL 5.6.6.

For each account, ALTER USER expires its password. For example:

ALTER USER 'jeffrey'@'localhost' PASSWORD EXPIRE;

The account name uses the format described in
http://dev.mysql.com/doc/refman/5.6/en/account-names.html. If you
specify only the user name part of the account name, a host name part
of '%' is used.

Password expiration for an account affects the corresponding row of the
mysql.user table: The server sets the password_expired column to 'Y'.

*Warning*: In MySQL 5.6.6, ALTER USER also sets the Password column to
the empty string, so do not use this statement until 5.6.7.

After an account's password has been expired, all operations performed
in subsequent connections to the server using the account result in an
error until the user issues a SET PASSWORD statement to establish a new
account password:

mysql> SELECT 1;
ERROR 1820 (HY000): You must SET PASSWORD before executing this statement

mysql> SET PASSWORD = PASSWORD('new_password');
Query OK, 0 rows affected (0.01 sec)

mysql> SELECT 1;
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)

As of MySQL 5.6.8, this restricted mode of operation also permits SET
statements, which is useful if the account password uses a hashing
format that requires old_passwords to be set to a value different from
its default.

It is also possible for an administrative user to reset the account
password, but any existing connections for the account remain under
restriction. Clients using the account must disconnect and reconnect
before statements can be executed successfully.

It is possible after password expiration to "reset" a password by using
SET PASSWORD to set it to its current value. As a matter of good
policy, it is preferable to choose a different password.

URL: http://dev.mysql.com/doc/refman/5.6/en/alter-user.html

