Why does mysql use primary key id and pid city index, id > 10 for index time > 10 for index?

  mysql, question

Why are both primary key id and pid indexes, id > 10 goes index time > 10 does not go index? Their values are the same.
I found that id > or < how to go through the index

Do you know what an index is?

Is the time field indexed?
No index has been created. How to get to the index?