Question

I have several entities which respresent different types of users who need to be able to log in to a particular system. Additionally, they have different types of information associated with them.

For example: a “general user”, which has an e-mail address and “admin user”, which has a workstation number (note that this a hypothetical case). Both entities also share common properties like first name, surname, address and telephone number. Finally, they naturally need to have a (unique) user name and a password to log in.

In the application, the user just has to fill in his user name and password, and the functionality of the application changes slightly according to the type of the user. You can imagine that the username needs to be unique for this work.

How should I model this effectively?

I can’t just create two tables, because then I can’t force a unique constaint on the user name.

I also can’t put them all in just one table, because they have different types of specific information associated to them.

I think I might need 3 seperate tables, one for “users” (with user name and password), one for the “general users” and another one for the “admin users”, but how would the relations between these work? Or is there another solution?

(By the way, the target DBMS is MySQL, so I don’t think generalization is supported in the database system itself).

Answer 1

Your 3 tables approach seems Ok.
In users table have only ID, username, password,usertype.
In general users table have ID, UserID (from users table), other fields.
Same thing for admin users.

Usertype field will tell you from what table to search for additional info

if(usertype==admin)
  select * from  admins where userid=:id;
else    
  select * from  general where userid=:id;