Miscellaneous Functions • UUID() •The fourth number preserves temporal uniqueness in case the timestamp value loses monotonicity (for example, due to daylight saving time). •The first three numbers are generated from the low, middle, and high parts of a timestamp. The high part also includes the UUID version number. •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 device has no Ethernet card, or it is unknown how to find the hardware address of an interface on the host operating system). In this case, spatial uniqueness cannot be guaranteed. Nevertheless, a collision should have  very  low probability. The MAC address of an interface is taken into account only on FreeBSD, Linux, and Windows. On other operating systems, MySQL uses a randomly generated 48-bit number. mysql>  SELECT UUID(); -> ’6ccd780c-baba-1026-9564-5b8c656024db’ Warning Returns a Universal Unique Identifier (UUID) generated according to RFC 4122, “A Universally Unique IDentifier (UUID) URN Namespace”  (http://www.ietf.org/rfc/rfc4122.txt). 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 devices not connected to each other. Although  UUID()  values are intended to be unique, they are not necessarily unguessable or unpredictable. If unpredictability is required, UUID values should be generated some other way. UUID()  returns a value that conforms to UUID version 1 as described in RFC 4122. The value is a 128- bit number represented as a  utf8  string of five hexadecimal numbers in  aaaaaaaa-bbbb-cccc- dddd-eeeeeeeeeeee  format: To convert between string and binary UUID values, use the  UUID_TO_BIN()  and  BIN_TO_UUID() functions. To check whether a string is a valid UUID value, use the  IS_UUID()  function. This function is unsafe for statement-based replication. A warning is logged if you use this function when binlog_format  is set to  STATEMENT . • UUID_SHORT() Returns a “short”  universal identifier as a 64-bit unsigned integer. Values returned by  UUID_SHORT() differ from the string-format 128-bit identifiers returned by the  UUID()  function and have different 2451