The answer is to set 'Assume Referential Integrity' on the relationship between the large dimension table and the fact table. This setting is correct because it tells Power BI that every value in the foreign key column of the fact table has a matching entry in the dimension table, allowing the engine to generate INNER JOINs instead of the default, more resource-intensive OUTER JOINs when the slicer filters the dimension. On the PL-300 exam, this scenario tests your understanding of DirectQuery optimization techniques that require no changes to the underlying SQL Server source. A common trap is to consider reducing column cardinality or switching to dual storage, but those either compromise accuracy or are incompatible with pure DirectQuery. Remember the memory tip: "Assume Integrity = Inner Join Efficiency" — when you can guarantee referential integrity, you unlock faster query folding for slicer interactions on large tables.
PL-300 Visualize and analyze the data Practice Question
This PL-300 practice question tests your understanding of visualize and analyze 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 Power BI report that uses DirectQuery to a SQL Server database. Users report that the report is slow when filtering by a slicer on a large dimension table. You need to improve performance without changing the data source. Which approach should you take?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set 'Assume Referential Integrity' on the relationship between tables
Option C is correct because setting 'Assume Referential Integrity' allows Power BI to use more efficient queries (INNER JOIN instead of OUTER JOIN) when filtering, which improves performance. Option A is wrong because aggregations are not supported in DirectQuery for this scenario. Option B is wrong because reducing cardinality may affect accuracy. Option D is wrong because dual storage mode does not apply to DirectQuery sources.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Create an aggregation table on the dimension
Why it's wrong here
Aggregations are not supported for DirectQuery on dimension tables.
✗
Change the storage mode of the dimension table to Dual
Why it's wrong here
Dual mode is not applicable for DirectQuery sources.
✓
Set 'Assume Referential Integrity' on the relationship between tables
Why this is correct
This enables optimized query execution in DirectQuery.
Related concept
Read the scenario before looking for a memorised answer.
✗
Reduce the cardinality of the slicer field by grouping values
Why it's wrong here
This may reduce accuracy and not address the root cause.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which PL-300 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Visualize and analyze the data — This question tests Visualize and analyze the data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set 'Assume Referential Integrity' on the relationship between tables — Option C is correct because setting 'Assume Referential Integrity' allows Power BI to use more efficient queries (INNER JOIN instead of OUTER JOIN) when filtering, which improves performance. Option A is wrong because aggregations are not supported in DirectQuery for this scenario. Option B is wrong because reducing cardinality may affect accuracy. Option D is wrong because dual storage mode does not apply to DirectQuery sources.
What should I do if I get this PL-300 question wrong?
Identify which PL-300 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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