How to generate globally unique ids for different tables of the same database? In a production system on SQL Server all ids (mostly PKs) in all tables are generated automatically and I am informed that they are unique globally. I mean no 2 ids are the same in the database, even if tables are different. I want to know how this can be done? If there are multiple ways please list them all. Thanks.
Back in the day we had an ID table. Single column, single row with an int value. Every transaction first updated that table to get a new value, which was then used wherever it was needed. This was, of course, a great source of concurrency errors.

Later, sequences were introduced. A single sequence used across the whole database would show the behaviour you describe. There's an example in the documentation that illustrates this:

CREATE TABLE Audit.ProcessEvents
(
    EventID int DEFAULT (NEXT VALUE FOR Audit.EventCounter), -- same sequence, different table
    &lt;other columns&gt;
);

CREATE TABLE Audit.ErrorEvents
(
    EventID int DEFAULT (NEXT VALUE FOR Audit.EventCounter), -- same sequence, different tables
    &lt;other columns&gt;
);



I've edited the example to highlight this usage.

An identical outcome could be achieved by generating the globally unique numbers in the application code, before they are passed to the database. Were I to implement this I imagine it would be as a static method of some utility class compiled into the executable (though other implementations would be possible). Say the application needs to write a customer's details to the database. As it is marshaling the customer name, address, telephone number etc. it also generates a new global ID. The ID is passed to the INSERT statement (or stored procedure) as just another parameter value.

Whether the ID values are produced by the application architectural tier or the database tier would depend on the specific design considerations. If the app can scale out coordination between instances becomes problematic. After an application re-start the code must figure out the next value to use. The DB server has these features, and others, written into it already.

What I would definitely not do is have the application call the database just for the next ID, then marshal that with the business data into an INSERT. That's too many round-trips to the database when only one is required.