Data engineering·Modelling for analysis
you joined on the email address, and then two people changed their email and one of them was reused by a new account.
Natural key
Also calledbusiness key, source key
The identifier the business already uses — an order number, an ISBN, a customer reference from the source system. It is meaningful, which makes it readable and makes it change: business keys get reissued, reformatted, and merged during acquisitions. Keep it on the dimension row so humans can find things and so loads can match on it, but do not make it the thing a billion fact rows point at.