Convert generalization in ERD to Relationnal Database having no additional column

Question

I've a quite simple problem but the litterature I came accross didn't seem to dwell on. Let's say I have an entity OFFER which represents an Offer on a Product, for each product, one offer can be "promoted" as BUY.

We can clearly see that a BUY is an OFFER.

But the odd thing is that there's no new column added so I wonder how I should represent it in Relationnal Database ? A new Table BUY having just the primary keys of OFFER ? A boolean field in OFFER saying whether it's an BUY or not ?

Answer 1

This kind of depends on more specifics to your use case, but generally speaking you probably can be fine with having a column in your Offers table to denote when a specific Offer is a buy, whether that's through a boolean based field e.g. IsBuy or a status field OfferStatus if you needed to cover multiple statuses of an Offer besides just buy.