T
Thomas Mercer-Hursh
Guest
Marian, while I tend to agree that the best possible design probably doesn't use this feature, I have seen lots of schemas that do. A classic is something like the invoice number corresponding to a order. Yes, better to use a join table and allow for many to many matches, but a lot of older schemas will put things like that right in the order. The invoice number is unknown when the order is created, but it is still a valid order. That index is also not used at that stage. And, the order number is used to locate the record. No one said we had to be talking about a primary index. Note that in many use cases it is also benign.
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