Primary Key versus Unique Constraint?

Question

I\'m currently designing a brand new database. In school, we always learned to put a primary key in each table.

I read a lot of articles/discussions/newsgroups posts

Answer 1

the thing is that a primary key can be one or more columns which uniquely identify a single record of a table, where a Unique Constraint is just a constraint on a field which allows only a single instance of any given data element in a table.

PERSONALLY, I use either GUID or auto-incrementing BIGINTS (Identity Insert for SQL SERVER) for unique keys utilized for cross referencing amongst my tables. Then I'll use other data to allow the user to select specific records.

For example, I'll have a list of employees, and have a GUID attached to every record that I use behind the scenes, but when the user selects an employee, they're selecting them based off of the following fields: LastName + FirstName + EmployeeNumber.

My primary key in this scenario is LastName + FirstName + EmployeeNumber while unique key is the associated GUID.