问题
Objective
Generate a unique 16-character key, to use as a batch name, that doesn't require any type of storage (e.g. a unique counter).
Background
I have a Windows service that runs every 30 seconds. I picks up messages off of an MQ and processes them in a batch. One of the service calls I'm making is requiring a 16-character batch name now. They don't care what the batch name is, it just needs to be unique across all batches.
Question
If I generate a Guid, can I use the first or last 16 characters of that string and it still be unique for my needs?
回答1:
No is the simple answer. Why not use the date/time?
For example, here's some Oracle generated GUIDs
D71CDF38BB3B6026E0430A9A9A286026
D71CDF38BB3C6026E0430A9A9A286026
D71CDF38BB3D6026E0430A9A9A286026
D71CDF38BB3E6026E0430A9A9A286026
D71CDF38BB3F6026E0430A9A9A286026
D71CDF38BB406026E0430A9A9A286026
回答2:
No.
Raymond Chen explains why in great detail in GUIDs are globally unique, but substrings of GUIDs aren't.
However, if you are running this on a single machine, then you don't need your ID to be globally unique - merely locally unique. Therefore, you can drop the MAC address requirement from the GUID algorithm he describes. Also, if you know that only one will be generated every 30 seconds, you can drop the collision part of the algorithm. This pretty much leaves you using the date-time as qujck suggests.
来源：https://stackoverflow.com/questions/15293487/can-i-use-the-first-or-last-16-characters-of-a-guid-and-it-still-be-unique