Quick Answer
The answer is Whole Number. This is the correct data type for a key column in Power BI because relationship keys require exact matching and efficient indexing, which only integer-based types like Whole Number can reliably provide without the precision issues or decimal variations that Decimal or Text types introduce. On the Microsoft Power BI Data Analyst PL-300 exam, this concept tests your understanding of data modeling fundamentals, often appearing in scenario-based questions where you must choose the optimal data type for a primary key used in relationships; a common trap is selecting Text because it can store unique values, but Whole Number is far more performant for joins and lookups. Remember that Power BI treats Whole Number as a 64-bit integer, making it the fastest type for key operations. A simple memory tip: for keys, think “whole, not partial”—Whole Number ensures every value is a clean, exact match.
This PL-300 practice question tests your understanding of prepare 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.
You have a column 'ProductID' that contains integers. You need to ensure that this column is used as a key in relationships. What data type should the column have?
Decimal Number.
Why wrong: Decimal is not needed for integer keys.
Text.
Why wrong: Text can be used but is less efficient.
Whole Number.
Whole Number (integer) is optimal for key columns.
Binary.
Why wrong: Binary is for images or files, not keys.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Whole Number.
Option C is correct because in Power BI, relationship keys must be of a data type that supports exact matching and efficient indexing. Whole Number (integer) is the optimal type for primary keys in relationships, as it ensures unique, non-decimal values that Power BI can use for fast lookups and joins without precision issues.
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.
Decimal Number.
Why it's wrong here
Decimal is not needed for integer keys.
Text.
Why it's wrong here
Text can be used but is less efficient.
Whole Number.
Why this is correct
Whole Number (integer) is optimal for key columns.
Related concept
Read the scenario before looking for a memorised answer.
Binary.
Why it's wrong here
Binary is for images or files, not keys.
Common exam traps
The trap here is that candidates may think Text is always acceptable for keys (since it can hold any value), but the question specifically tests the optimal data type for integer-based keys in Power BI relationships, where Whole Number is the correct and most efficient choice.
Detailed technical explanation
Under the hood, Power BI's VertiPaq engine stores Whole Number columns as compressed integers, enabling hash-based joins that are extremely fast. Using Decimal Number for keys would force floating-point comparisons, which are slower and risk rounding errors (e.g., 1.0 vs 0.9999999). In real-world scenarios, using Text for integer IDs increases storage size and degrades query performance due to string comparison overhead.
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
Prepare the data — This question tests Prepare the data — Read the scenario before looking for a memorised answer..
The correct answer is: Whole Number. — Option C is correct because in Power BI, relationship keys must be of a data type that supports exact matching and efficient indexing. Whole Number (integer) is the optimal type for primary keys in relationships, as it ensures unique, non-decimal values that Power BI can use for fast lookups and joins without precision issues.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 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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