The correct answer is to remove duplicate rows from the CustomerID column in the dimension table. This is necessary because Power BI relationships require a unique column on at least one side of the relationship, typically the dimension table, to enforce a one-to-many cardinality. By eliminating duplicates from the dimension table, you ensure that each CustomerID appears only once, allowing the relationship to the fact table to function correctly and maintain referential integrity. On the Microsoft Power BI Data Analyst PL-300 exam, this scenario tests your understanding of data modeling fundamentals, specifically the distinction between dimension and fact tables. A common trap is attempting to remove duplicates from the fact table, which would destroy transactional granularity; instead, always clean the dimension side. Remember the memory tip: "Dim is unique, Fact repeats" — dimension tables hold unique identifiers, while fact tables hold multiple transactions tied to those identifiers.
PL-300 Prepare the data Practice Question
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 are preparing data in Power BI Desktop. You have a table with a column 'CustomerID' that contains duplicate values. You need to create a relationship to another table that also has 'CustomerID'. However, the relationship requires unique values in at least one of the tables. What should you do?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove duplicate rows from the 'CustomerID' column in the dimension table.
Option D is correct because to create a relationship in Power BI, at least one table must have unique values in the column used for the relationship. By removing duplicate rows from the 'CustomerID' column in the dimension table (which should contain unique identifiers), you ensure that the dimension table has unique values, allowing a one-to-many relationship to be established with the fact table. This is a standard data modeling practice in Power BI to enforce referential integrity.
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 a composite key using multiple columns.
Why it's wrong here
Composite keys still require uniqueness; duplicates in the composite key would still cause issues.
✗
Use the 'Merge Queries' feature to combine the tables into one.
Why it's wrong here
Merging does not create a relationship; it combines tables horizontally.
✗
Change the data type of 'CustomerID' to text.
Why it's wrong here
Data type change does not affect duplicate values.
✓
Remove duplicate rows from the 'CustomerID' column in the dimension table.
Why this is correct
Removing duplicates ensures uniqueness for the relationship.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often think changing data types or merging tables will solve the uniqueness issue, but Power BI specifically requires unique values in at least one table for a relationship, and only removing duplicates directly addresses that requirement.
Detailed technical explanation
How to think about this question
In Power BI, relationships are based on the concept of cardinality, where a one-to-many relationship requires the 'one' side to have unique values. The 'Remove Duplicates' operation in Power Query (M language) uses the Table.Distinct function, which removes rows based on duplicate values in selected columns, ensuring the dimension table has a unique key. This is critical for star schema design, where dimension tables should contain unique identifiers to enable efficient filtering and aggregation.
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.
TExam Day Tips
→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 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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Prepare the data — This question tests Prepare the data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Remove duplicate rows from the 'CustomerID' column in the dimension table. — Option D is correct because to create a relationship in Power BI, at least one table must have unique values in the column used for the relationship. By removing duplicate rows from the 'CustomerID' column in the dimension table (which should contain unique identifiers), you ensure that the dimension table has unique values, allowing a one-to-many relationship to be established with the fact table. This is a standard data modeling practice in Power BI to enforce referential integrity.
What should I do if I get this PL-300 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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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