When to split up models into multiple database tables?

Question

I\'m working with Ruby on Rails, but this question I think is broader than that and applies to database design generally.

When is it a good idea to split a single mo

Answer 1

Generally it is a good idea to put things which have a one-to-one relationship in the same table. Unless your userbase includes the Queen or Paddington Bear, a user has just one birthday, so that should be an attribute of the USERS table. Things which have a one-to-many relationship should be in separate tables. So, if a user can have multiple privacy settings by all means split them out.

Splitting one table into several tables can make queries more complicated or slower, if we want to retrieve all the user's information at once. On the other hand if we have a set of attributes which is only ever queried or updated in a discrete fashion then having a separate table to hold that data is a sound idea.