Why Keys Are Important
Keys are crucial to a table structure for the following reasons:
They ensure that each record in a table is precisely identified. As you already know, a table represents a singular collection of similar objects or events. (For example, a CLASSES table represents a collection of classes, not just a single class.) The complete set of records within the table constitutes the collection, and each record represents a unique instance of the table's subject within that collection. You must have some means of accurately identifying each instance, and a key is the device that allows you to do so.
They help establish and enforce various types of integrity. Keys are a major component of table-level integrity and relationship-level ...