The principle of generating an id for an order?

Question

Software design

By what principle is it worth generating an order number and at the same time writing it to the database?

Answer 1

Id, which is the primary key in the orders table, is sufficient

Answer 2

random of course

Answer 3

if an order can be viewed by its id on the Internet without registration and SMS, and it should not be possible to view other people's orders, I would use the current date and a 9-character random number when generating the id, that is,
20200728123456789

Answer 4

Depending on the purpose, it is clear that the database has a unique id, but for the client it can contain anything, for example, the id of the outlet + serial number