I am trying to develop a system to assign room numbers to tenants of a hostel upon registration, using the auto increment feature of sql.

However, it automatically increases by one after every entry. Because the hostel accommodates four people in one room, I want to change this to 4, so that after every 4 entries I get only one id/room number. 

How do I go about this? I am using php and sql. If the autoincrement feature is not possible can you please suggest another way to achieve this? Thanks.