---
title: "Define fact table"
subject: "Data Mining"
chapter: 1
key: "semester_7/data_mining:define-fact-table"
source: https://www.bctengineer.com/q/semester_7/data_mining/define-fact-table
site: BCT Engineering
---

# Define fact table

Data Mining · Chapter 1: Introduction

- Asked in: year not given
- Video: [Fact table and Dimension table | Data Warehousing](https://www.youtube.com/watch?v=dKyA6oBlKwo) — Kishan Mashru
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/data_mining/define-fact-table
- Whole chapter: https://www.bctengineer.com/md/semester_7/data_mining/chapter-1

## Question

Define Fact table with example.

## Short answer

A fact table is the central table in a dimensional schema storing numeric measures of a business process and foreign keys to dimensions at a defined grain. Example: Sales_Fact(time_key, item_key, branch_key, customer_key, units_sold, dollars_sold) records each sale with measures units_sold and dollars_sold linked to time, item, branch, and customer dimensions.

## Answer

A **fact table** is the central table of a dimensional (star/snowflake) schema. It stores the **measures** (numeric, usually additive values) of a business process, together with **foreign keys** to the dimension tables. Each row is one fact at the chosen grain. It is usually the largest table and grows continuously.

**Example**: `Sales_Fact(time_key, item_key, branch_key, customer_key, units_sold, dollars_sold)`.
Here `units_sold` and `dollars_sold` are the measures and the four keys point to the time, item, branch and customer dimensions. One row records the sale of an item on a day at a branch to a customer.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What does a fact table store?
   A. Numeric measures with foreign keys to dimensions
   B. Only keys
   C. Descriptive text only
   D. Metadata
   Answer: A. Measures plus foreign keys. (Key point: Fact table content)

2. What does each fact row represent?
   A. A dimension
   B. One fact at the chosen grain
   C. An entire table
   D. A schema
   Answer: B. A row records one event at the chosen grain. (Key point: Grain)

3. In Sales_Fact, which are measures?
   A. branch_key
   B. time_key
   C. item_key
   D. units_sold and dollars_sold
   Answer: D. The numeric values are measures; keys point to dimensions. (Key point: Example measures)

## Related in Data Mining

- [OLAP vs OLTP; OLAP operations, fact, dimension](https://www.bctengineer.com/question.md?key=semester_7%2Fdata_mining%3Aolap-oltp-operations-fact-dimension) — Data Mining, chapter 2
- [OLAP vs OLTP; schema, fact, dimension](https://www.bctengineer.com/question.md?key=semester_7%2Fdata_mining%3Aolap-oltp-schema-fact-dimension) — Data Mining, chapter 2