Answer 1

A surrogate key is an artificial key that is unique, system-generated, not corresponding to actual data, and not manipulable by the user. Usually a sequential number (-> column with AUTO_INCREMENT). A surrogate key is usually a primary key (that's its main purpose). Even if all your columns can have duplicate values (ie none is suitable to be the primary key), you can add a surrogate key and define it as the primary key. Basically an id column.