Syntax:
MD5(str)

Calculates an MD5 128-bit checksum for the string. The value is
returned as a binary string of 32 hex digits, or NULL if the argument
was NULL. The return value can, for example, be used as a hash key. See
the notes at the beginning of this section about storing hash values
efficiently.

URL: http://dev.mysql.com/doc/refman/5.0/en/encryption-functions.html

