BCS 260 Lecture Notes - Lecture 2: Compound Key, Foreign Key, Referential Integrity
Document Summary
Sometimes we have relations that correspond to real-world object where the real-world relationship is reflected inthe database. We sometimes need to split a relation into multiple relations. We will discuss this in the next few weeks. Interestingly, you will often find that these both apply, and a decomposed relation ends up as it should be with every relation representing a single entity or theme. Obviously, it"s a candidate for a primary key . A special relational database table column (or combination of columns) designated to uniquely identify all table records: we can have multiple candidate keys. We choose a single candidate key to make it the primary key . We typically use this key in other tables to refer to this table: theoretically we could use different candidate keys for each relation, but typically this is not done (for practical reasons) and some software won"t allow it. A primary key can be a composite key.
