fact table

Fact Table

The table at the center of a star schema that holds the events or transactions a business wants to measure — orders, page views, payments, sign-ups.

When you'd see it: Anywhere analysts count, sum, or average something. Fact tables are usually long and skinny — millions or billions of rows, mostly numbers and foreign keys pointing at dimension tables. "How many orders did we ship last week" is a fact-table question.

Why it matters: The fact table is where the business's measurable activity actually lives. The quality of every downstream metric — revenue, conversion, retention — depends on the fact table capturing the right events at the right grain. Get the grain wrong and the whole reporting layer drifts.

Common mistakes: Confusing fact tables with detail tables. A fact table records what happened; a detail table might also include who did it, where, and why — but in a clean star schema, those descriptions live in dimension tables, not fact tables.

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