Quick Answer
The answer is CustomerID. In a properly designed star schema, fact tables should only contain foreign keys to dimension tables and quantitative, measurable data like Quantity and SalesAmount, while descriptive attributes such as CustomerID belong in a dedicated dimension table. Including CustomerID directly in the fact table would break the star schema’s normalization, making it harder to filter by customer attributes or navigate hierarchies like customer region or segment. On the PL-300 exam, this concept is frequently tested by presenting a list of columns and asking which one violates the fact table design—the common trap is mistaking a foreign key for a measure, but remember that any ID that represents a business entity (customer, product, date) is a dimension key, not a fact column. A quick memory tip: if the column describes who, what, or when, it belongs in a dimension; if it measures how much or how many, it belongs in the fact table.
This PL-300 practice question tests your understanding of model the data. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A data analyst is designing a star schema in Power BI. The model includes a table named 'Orders' with columns: OrderID, CustomerID, OrderDate, ProductID, Quantity, and SalesAmount. Which column should NOT be included in the fact table to maintain a proper star schema?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "NOT"
Why it matters: Negative qualifier — you are looking for the one option that does NOT apply. Most options will be true; only one is false for this scenario.
Quantity
Why wrong: Quantity is a numeric measure appropriate for fact tables.
SalesAmount
Why wrong: SalesAmount is a numeric measure typically stored in fact tables.
CustomerID
CustomerID is a foreign key to a dimension table; it should be stored in the fact table to link to the Customer dimension.
OrderID
Why wrong: OrderID is a unique identifier for each transaction row in the fact table.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
CustomerID
In a star schema, fact tables store quantitative, measurable data (measures) and foreign keys to dimension tables. CustomerID is a descriptive attribute that belongs in a Customer dimension table, not in the fact table. Including it in the fact table would violate normalization principles and reduce the model's flexibility for filtering and hierarchy navigation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Quantity
Why it's wrong here
Quantity is a numeric measure appropriate for fact tables.
SalesAmount
Why it's wrong here
SalesAmount is a numeric measure typically stored in fact tables.
CustomerID
Why this is correct
CustomerID is a foreign key to a dimension table; it should be stored in the fact table to link to the Customer dimension.
Clue confirmation
The clue word "NOT" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
OrderID
Why it's wrong here
OrderID is a unique identifier for each transaction row in the fact table.
Common exam traps
The trap here is that candidates often mistake any ID column as a fact table key, but CustomerID is a foreign key that should be moved to a dimension table, whereas OrderID is the fact table's grain key and is correctly placed.
Detailed technical explanation
Under the hood, Power BI's VertiPaq engine compresses fact tables more efficiently when they contain only foreign keys and numeric measures, as these data types benefit from value encoding and run-length encoding. Including high-cardinality string columns like CustomerID (if stored as text) would degrade compression and query performance. In a real-world scenario, a fact table with CustomerID instead of a foreign key would prevent users from slicing by customer attributes (e.g., region, segment) without duplicating that data across every row.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
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FAQ
Model the data — This question tests Model the data — Read the scenario before looking for a memorised answer..
The correct answer is: CustomerID — In a star schema, fact tables store quantitative, measurable data (measures) and foreign keys to dimension tables. CustomerID is a descriptive attribute that belongs in a Customer dimension table, not in the fact table. Including it in the fact table would violate normalization principles and reduce the model's flexibility for filtering and hierarchy navigation.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "NOT". Negative qualifier — you are looking for the one option that does NOT apply. Most options will be true; only one is false for this scenario.
Read the scenario before looking for a memorised answer.
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which THREE of the following are benefits of using a star schema in Power BI? (Select three.)
mediumWhy A: Option A is correct because star schemas reduce the number of table joins and filter context complexity, which simplifies DAX formulas. Measures and calculated columns in Power BI rely on unambiguous relationships; a star schema ensures each fact table connects to dimension tables via one-to-many relationships, allowing DAX to propagate filters automatically without complex cross-filtering logic.
Last reviewed: Jun 11, 2026
This PL-300 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PL-300 exam.
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