Glossary

Fact Table

A fact table is the table in a dimensional model that stores measurements: the numeric events a business wants to analyse, such as sales amounts, quantities, or durations. Each row records one measurement event at a declared grain — one order line, one payment, one sensor reading — and carries the numeric measures plus foreign keys to the dimension tables that give those numbers context.

Fact tables are long and narrow: billions of rows, few columns. They come in three types — transaction, periodic snapshot, and accumulating snapshot — distinguished entirely by what one row represents. The discipline that keeps a fact table trustworthy is grain: every measure in the table must be true at the declared grain, or aggregates silently double-count.

Go deeper: Fact Table vs Dimension Table: The Core Distinction