Question

For example, lets say I have an entity called user and an entity called profile_picture. A user may have none or one profile picture.

So I thought, I would just create a table called “user” with this fields:

user: user_id, profile_picture_id
(I left all other attributes like name, email, etc. away, to simplify this)

Ok, so if an user would have no profile_picture, it’s id would be NULL in my relational model. Now someone told me that I have to avoid setting anything to NULL, because NULL is “bad”.

What do you think about this? Do I have to take off that profile_picture_id from the user table and create a link-table like user__profile_picture with user_id, profile_picture_id?

Which would be considered to be “better practice” in database design?

Answer 1

This is a perfectly reasonable model. True, you can take the approach of creating a join table for a 1:1 relationship (or, somewhat better, you could put user_id in the profile_picture table), but unless you think that very few users will have profile pictures then that’s likely a needless complication.

Readability is an important component in relational design. Do you consider the profile picture to be an attribute of the user, or the user to be an attribute of the profile picture? You start from what makes logical sense, then optimize away the intuitive design as you find it necessary through performance testing. Don’t prematurely optimize.