Just out of curiosity, I generated 40,000 numbers using SYS(3) in a loop on a 450 mhz machine (NT4.0, 96 mb ram) and I didn't get any duplicates. Strange...


>Hi Garrett,
>
>>If I understand correctly, CoCreateGuid() keys off the MAC address of the Ethernet card, if one exists, and is therefore guaranteed to be unique between machines with cards. Within a machine, I suppose you could defeat it by resetting the system clock, and running it at exactly the same time.
>
>>As I understand it, if the machine doesn't have an Ethernet card, it uses some other algorithm that is unlikely to produce duplicates.
>
>CoCreateGuid(), according to the documentation, calls UuidCreate(), which uses the Ethernet or token ring hardware address. That function can return a RPC_S_UUID_NO_ADDRESS error if it cannot get this information.
>
>>BTW, the Identity columns in SQL Server 7 are supposed to be GUIDs, so that every row is unique globally, not merely within a table.
>
>As an FYI for other readers of this thread, here's what the documentation says about CoCreateGuid():
>
>"The CoCreateGuid function calls the RPC function UuidCreate, which creates a GUID, a globally unique 128-bit integer. Use the CoCreateGuid function when you need an absolutely unique number that you will use as a persistent identifier in a distributed environment.To a very high degree of certainty, this function returns a unique value - no other invocation, on the same or any other system (networked or not), should return the same value."
>
>I think that the above explains pretty well why SQL Server 7 uses them.
>
>Regards,