Editing Composite key (section)

== Example ==
An example is an entity that represents the modules each student is attending at University. The entity has a {{lang|mis|studentID}} and a {{lang|mis|moduleCode}} as its [[primary key]]. Each of the attributes that makes up the primary key is a simple key because each represents a unique reference when identifying a student in one instance and a module in the other, so this key is a compound key.

In contrast, using the same example, imagine we identified a student by their {{lang|mis|firstName}} + {{lang|mis|lastName}} (assuming that people must have different names). In a table representing students our primary key would now be {{lang|mis|firstName}} + {{lang|mis|lastName}}. Because students can have the same {{lang|mis|firstName}} or the same {{lang|mis|lastName}} these attributes are not simple keys.  The primary key {{lang|mis|firstName}} + {{lang|mis|lastName}} for students is a composite key.