Yeah this is nice - also helps with grepping dump files.
replyHow is this done?
replyThey just mean you catch incorrect joins more easily because there is usually no overlap in keys between unrelated tables. Using int, you’re usually going to have some shared values between two unrelated tables.
replyStatistically impossible to inadvertently generate a collision using UUID keys. UUID is designed to be unique when generated across any computer system. Practically speaking if you have an exactly matching pair of UUIDs from disparate system you have found the exact record match. The name gives a hint "Universally unique identifier". -Not a cryptographer.
replyIt definitely is possible, just very improbable
replyThat’s probably what’s meant by statistically impossible.
replydeleted
replyThe U means if you join the wrong table your join will always come up empty.
replyIt does not actually make it impossible to query the wrong table it just tells you quickly when you’ve done so.
You can achieve this with numeric sequences too, by having a consistent step and unique offset in all your sequences. For example, if you will never exceed 16 types, reserve four bits as the type discriminant. (You don’t have to use powers of two, but it may be convenient.)
replyAll sequences use step 16.
Type A has discriminant/offset 0, yielding IDs {0, 16, 32, 48, 64, …}.
Type B has discriminant/offset 1, mapping to IDs {1, 17, 33, 49, 65, …}.
All the way up to Type P with discriminant/offset 15 and IDs {15, 31, 47, 63, 79, …}.
This is also trivially invertible so that you can determine the type from the ID.
A more common approach is to make IDs opaque strings and put a type prefix—A0, B12, P34, that kind of thing. But this way you can keep it as a number, if you wish.