Primary and Surrogate Keys
Learn about keys in PostgreSQL.
We'll cover the following...
Primary key
Primary keys are a database constraint allowing us to implement the first and second normal forms. The first rule to follow to reach the 1NF says, “there are no duplicated rows in the table.”
A primary key ensures two things:
-
The attributes that are part of the primary key constraint definition are not allowed to be
null. -
The attributes that are part of the primary key are unique in the table’s content.
To ensure that there is no duplicated row, we need the two guarantees. Comparing null values in SQL is a complex matter—as seen in Three-Valued Logic chapter—and rather than argue if the no-duplicate rule applies to null = null (which is null) or to null is not null (which is false), a ...