Separate or Combine 2 Tables with Similar Attributes?

I have two kind of users in my business system: Customer and Employee.
Both user have Username, Password, Fullname, Phone Number, Email, and other similar attributes.


I have a difficulty to determine which is better to merge
Customer and Employee on one table (for example I store in User table) or separate each entities on different table?

On my case, the Customer has additional attributes that the Employee doesn't had (for example: NewsUpdateSubscription). And also for Employee, it has additional attributes that Customer doesn't had (for example: Salary). What is the best practice for this case? Thanks in advance.

While the names for these attributes may be the same, it's very likely that you'll want to store different values depending upon whether a person is a customer or an employee.

For example, if I work for a company but also use their website to purchase their products (so I'm an employee and a customer), when purchasing products I'll want to enter my personal phone number, email address etc. Whereas my employee record will need to store my work issued email address, phone and so on.

If you create a single users table to store all the common fields, if I want to change my contact number for purchases I've made, then my employee record will also be updated. If HR/IT use this information to know which phone I should return when leaving the company it could cause issues down the line if I'm free to change it in the customer context.

Therefore I'd recommend creating separate tables. The exception would be if you were in the unusual situation where your employees are your customers (which may be the case for an internal purchases application).

StackExchange Database Administrators Q#31193, answer score: 4