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.

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

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

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

Each 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'.

A client session operates in restricted mode if the account password
has been expired. In restricted mode, operations performed in the
session 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 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 sessions for the account remain restricted.
Clients using the account must disconnect and reconnect before
statements can be executed successfully.

*Note*: It is possible to "reset" a password with SET PASSWORD by
setting 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

