Generating sequential numbers in multi-user saas application

Question

How do people generate auto_incrementing integers for a particular user in a typical saas application?

For example, the invoice numbers for all the invoices for a partic

Answer 1

You could introduce another table associated with your "users" table that tracks the most recent invoice number for a user. However, reading this value will result in a database query, so you might as well just get a count of the user's invoices and add one, as you suggested. Either way, it's a database hit.