Replacement key, Alternate key, and Surrogate key
WHAT IS A REPLACEMENT KEY INDEX?
While a surrogate key is great for lookup and database performance, it is not useful for the end-user because it gives no indication of the table’s purpose, or what related tables it is linked to. For this reason, Dynamics 365 Finance & Operations has added the ‘Replacement Key’ index property for tables. The replacement key index is a dropdown of alternate keys that have been specified for the table. There can be any number of alternate keys for a table but only a single replacement key. More than one field can be specified under a replacement key, and it is these fields that will be displayed to the end-user on a form instead of the surrogate key field.A replacement key is an alternate key that the system can display on forms instead of a meaningless numeric primary key value. Each table can have a maximum of one replacement key.
The replacement key is chosen by setting the ReplacementKey property on the table. The drop-down list offers every alternate key as an available value.