Alternate key & Replacement key
But it also has two unique keys, that could be used as the primary key, therefore they're alternate keys.
One of them, HcmWorker_AX2, contains a human-readable value, namely the personnel number. That's a good choice when we want to display something to users, allow them to select a worker from a lookup and so on. Working with the primary key, RecId, wouldn't make sense, so we set HcmWorker_AX2 as the replacement key, and it will be automatically used by reference group controls.
