Primary Key

• Unique identifier which identifies the row in the table. Generally a surrogate key.
• Because it is unique, each table
  • primary key values must not be repeated
  • can be a column or a set of columns to act as the unique identifier

Surrogate Key

Candidate Keys

• the Candidate keys uniquely identify the rows of a table. The primary key is chosen from the set of candidate keys

Alternate Keys

• the candidate keys that were not chosen to be the primary key is called the alternate key.

Foreign Keys

• The Foreign Keys in a table match to another primary key in another table. Because the primary key is unique in one table, the foreign key shall also be unique in another table.
• Foreign keys help maintain data integrity, and create referential links.