SQL: Visual QuickStart Guide

Normalization

You may have wondered why I don’t consolidate all information about books (or any entity type) into a single table. It’s possible, but the resulting table would be loaded with duplicate data; each book (row) would contain redundant author, publisher, and royalty details. Redundant data is the enemy of database administrators: It causes databases to grow wildly large, it slows queries, and it’s a maintenance nightmare. (When someone moves, you want to change her address in one place, not thousands of places.)

Normalization is the process—a series of steps—of modifying tables to reduce redundancy and inconsistency. After each step, the database is in a particular normal form. The relational model defines three normal forms, named ...