Recently I’ve been working with HES data on a project, and the current structure of tables we have is for each of the different datasets (Inpatients, Outpatients, Emeregency Care, etc.) we have a separate table for each financial year. Within these there will be a column like EPIKEY or ATTENDKEY which is the primary key in that table. This key is stored as a BIGINT.
This key restarts counting each year… well, sort of.