An account number is used to link sales records with customer records – and that’s about it. Best of all, everyone understands an account. Everyone knows how sales records can be attached to a customer based on the account field.
The field customer_id is a ‘primary key’ for the customer table. That means that it is a unique identifier. It is unique in that its uniqueness is enforced by the database. An account number is supposed to be unique, but it may not be.
Primary keys are what are used in database systems to link the data together. That’s all they do. One quirk about them is that they are never supposed to be viewed by the users.