Syntax:
UUID()

Returns a Universal Unique Identifier (UUID) generated according to
"DCE 1.1: Remote Procedure Call" (Appendix A) CAE (Common Applications
Environment) Specifications published by The Open Group in October 1997
(Document Number C706,
http://www.opengroup.org/public/pubs/catalog/c706.htm).

A UUID is designed as a number that is globally unique in space and
time. Two calls to UUID() are expected to generate two different
values, even if these calls are performed on two separate computers
that are not connected to each other.

A UUID is a 128-bit number represented by a utf8 string of five
hexadecimal numbers in aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee format:

o The first three numbers are generated from a timestamp.

o The fourth number preserves temporal uniqueness in case the timestamp
  value loses monotonicity (for example, due to daylight saving time).

o The fifth number is an IEEE 802 node number that provides spatial
  uniqueness. A random number is substituted if the latter is not
  available (for example, because the host computer has no Ethernet
  card, or we do not know how to find the hardware address of an
  interface on your operating system). In this case, spatial uniqueness
  cannot be guaranteed. Nevertheless, a collision should have very low
  probability.

  Currently, the MAC address of an interface is taken into account only
  on FreeBSD and Linux. On other operating systems, MySQL uses a
  randomly generated 48-bit number.

URL: http://dev.mysql.com/doc/refman/5.1/en/miscellaneous-functions.html

