Syntax:
OLD_PASSWORD(str)

OLD_PASSWORD() was added when the implementation of PASSWORD() was
changed in MySQL 4.1 to improve security. OLD_PASSWORD() returns the
value of the pre-4.1 implementation of PASSWORD() as a string, and is
intended to permit you to reset passwords for any pre-4.1 clients that
need to connect to your version 5.5 MySQL server without locking them
out. See http://dev.mysql.com/doc/refman/5.1/en/password-hashing.html.

As of MySQL 5.5.3, the return value is a nonbinary string in the
connection character set. Before 5.5.3, the return value is a binary
string.

URL: https://mariadb.com/kb/en/old_password/

