PL-300 Model the data Practice Question
You are designing a star schema for a sales analysis report. The source data includes Order Details, Products, Customers, and Dates. Which table should be the fact table?
⚠ Common exam trap
The trap here is that candidates often mistake dimension tables like Dates or Products as the fact table because they appear frequently in reports, but the fact table must contain the measurable events (e.g., sales transactions) that drive the analysis.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Order Details
In a star schema, the fact table stores quantitative, measurable data (metrics) and foreign keys linking to dimension tables. Order Details contains sales transactions with measures like quantity and revenue, making it the correct fact table for sales analysis.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Dates
Why it's wrong here
Dates should be modeled as a dimension table, not the fact table, because it contains date attributes such as year, quarter, month, and day that are used for filtering and grouping, not numeric additive measures. In a star schema, a fact table records business events and their measurable quantities; Dates lacks those measures. Additionally, Date dimensions often support role-playing behavior (e.g., Order Date, Ship Date) through multiple foreign keys, reinforcing its dimension role.
- ✗
Customers
Why it's wrong here
Customers is a dimension table because it stores descriptive, slowly changing attributes about each customer, such as name, address, segment, and region, which are used as filter criteria and row headers in reports. Fact tables should contain foreign keys and numeric measures; Customers has neither. Customer dimension design also involves surrogate keys to handle changes over time, such as tracking a customer moving from one region to another, which is a dimension-table characteristic, not a fact-table one.
- ✓
Order Details
Why this is correct
Order Details is the correct fact table because each row represents a line item from an order, the lowest grain of the sales process, and it holds numeric measures like quantity, unit price, and discount that can be aggregated with SUM and similar functions. It also contains foreign key columns (OrderID, ProductID, CustomerID, etc.) that link to the surrounding dimension tables, creating the star schema. The presence of both additive measures and multiple dimension keys is the defining property of a fact table.
- ✗
Products
Why it's wrong here
Products is a dimension table, not a fact table, because it provides descriptive attributes such as product name, category, color, and supplier, which are used to slice and filter the measures in the fact table. Product rows do not record individual sales events, and they lack numeric transactional measures like quantity sold or revenue. Instead, Products sits at the 'edge' of the star schema, connected to the central fact table via a foreign key, and is used to answer 'by product' business questions.
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