What is a Dimension Table?
A dimension table provides the description behind the analytic numbers. It describes the who, what, when, where and why behind the facts. Dimensions are normally broken down into groups (tables) and they contain several attributes (columns). Unlike a fact table the dimension table is not normalized. Generally, dimension tables have many columns but a limited amount of rows.
Dimension tables normally provide two purposes in a data warehouse, it can be used to filter queries and to select data.