dimension table

Dimension Table

A table that describes the people, products, dates, places, or categories referenced by a fact table — the context around the events.

When you'd see it: Every grouping or filtering question. "Orders by customer segment" needs a customer dimension. "Revenue by region by month" needs region and date dimensions. Dimension tables are usually wide and short — many columns describing each entity, but far fewer rows than the fact table.

Why it matters: Dimensions are how a business sees itself. The columns chosen for the customer dimension decide what questions about customers can be asked easily. Skimping on dimension design — fewer attributes, less history — quietly limits the analyses the company can ever run.

Common mistakes: Ignoring how dimensions change over time. A customer's segment, a product's price, an employee's manager — all of these change. Tracking those changes ("slowly changing dimensions") is what separates a usable warehouse from one that silently rewrites history every time the dimensions refresh.

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