Re: Three tables or one?

[Ndi Ekpenyong]

I have a slightly different situation. I have an entity which has 2 main subtypes. In total the entity has about 35 attributes, but the two subtypes share only 17 attributes while the other 18 attributes are specific to the subtypes. There may well be other subtypes in the future with fewer differentiating attributes. If I implement one table, there is bound to be a lot of blank fields depending on the subtype. It is said that it is more elegant to create a supertype table and then a view for every subtype (based on a discriminator column). But this does not really take away the blank column issue. Others propose that if there are few attributes at the supertype level and more at te subtype level, then a 2 table implementation is best. Especially as my attributes are (almost) split down the middle....so i am confused. However I find the 2 table implementation a lot simpler though not elegant.