Some sort of “different auto-increment indexes” per a primary key values

Question

I have got a table which has an id (primary key with auto increment), uid (key refering to users id for example) and something else which f

Answer 1

It is important to get your data types right.

What you are describing is a multi-part key. So use a multi-part key. Don't try to encode everything into a magic integer, you will poison the rest of your code.

If a record is identified by (entity_id,version_number) then embrace that description and use it directly instead of mangling the meaning of your keys. You will have to write queries which constrain the version number but that's OK. Databases are good at this sort of thing.

version_number could be a timestamp, as a_horse_with_no_name suggests. This is quite a good idea. There is no meaningful performance disadvantage to using timestamps instead of plain integers. What you gain is meaning, which is more important.

You could maintain a "latest version" table which contains, for each entity_id, only the record with the most-recent version_number. This will be more work for you, so only do it if you really need the performance.