Lecture 10/10/16 - Keys

A key is a value that uniquely indentifies every entry in a particular table. A candidate key is any field that will have a unique value for every record.

How a key is chosen

  • Unique, universal, permanent
  • Can be 'natural' EG, national insurance number
  • Key can be a set of columns
  • DBMS can automatically generate a key each time a new record is added to a table

What is a key used for?

Primary keys are used for indexing and searching purposes within its own table.