How NEWID() Works in SQL? Is it UNIQUE for Whole DB ?

If you use the built-in methods of uniqueidentifier generation (like newId() or C#'s Guid.NewGuid()), yes, it will be unique across databases, servers, countries, whatever.

In fact, that's one of the big uses of GUIDs - replication. If you have the same GUID in two databases, it's guaranteed that it was put there on purpose.

However, do note that GUIDs do have their shortcomings - they might make your indices perform worse (or at least require more maintenance), and they are bigger in general.

Also, GUIDs aren't entirely random - there's a few different GUID generating algorithms, some of which are inherently unique (e.g. using a MAC address as part of the GUID - MACs are unique by default, although you can override them manually) - so one part is unique per physical server, and the machine makes sure it doesn't use the same timestamp for two GUIDs. There's also sequential GUIDs (newSequentialId()), which are handy in avoiding index fragmentation (very useful for clustered indices of course) - do note that those depend on the MAC address of the computer, and they are predictable, so if you're making the GUID public, and you depend on them being "secret", you might not want to use those. Some GUID algorithms are more predictable than others.

also go through the below url:

https://dba.stackexchange.com/questions/152414/how-uniqueidentifier-in-sql-server-is-always-a-unique-value-globally

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Piyush Pansuriya8y ago
If you use the built-in methods of uniqueidentifier generation (like newId() or C#'s Guid.NewGuid()), yes, it will be unique across databases, servers, countries, whatever.

In fact, that's one of the big uses of GUIDs - replication. If you have the same GUID in two databases, it's guaranteed that it was put there on purpose.

However, do note that GUIDs do have their shortcomings - they might make your indices perform worse (or at least require more maintenance), and they are bigger in general.

Also, GUIDs aren't entirely random - there's a few different GUID generating algorithms, some of which are inherently unique (e.g. using a MAC address as part of the GUID - MACs are unique by default, although you can override them manually) - so one part is unique per physical server, and the machine makes sure it doesn't use the same timestamp for two GUIDs. There's also sequential GUIDs (newSequentialId()), which are handy in avoiding index fragmentation (very useful for clustered indices of course) - do note that those depend on the MAC address of the computer, and they are predictable, so if you're making the GUID public, and you depend on them being "secret", you might not want to use those. Some GUID algorithms are more predictable than others.

also go through the below url:
https://dba.stackexchange.com/questions/152414/how-uniqueidentifier-in-sql-server-is-always-a-unique-value-globally