Quick Answer
The answer is that the source table has duplicate 'OrderID' values. This is the most likely cause because the error message directly states that the column contains a duplicate value and is part of a primary key, and during a Power BI refresh, the data model enforces uniqueness on any column designated as a primary key. When importing from an Azure SQL database, if the source table violates this constraint by having duplicate keys, the refresh fails to maintain the required unique constraint. On the Microsoft Power BI Data Analyst PL-300 exam, this question tests your understanding of data refresh errors and source data integrity, often appearing as a trap where candidates might blame Power BI’s configuration rather than the source data. A common memory tip is to remember that Power BI is a mirror, not a filter—if the source has duplicates, the refresh will break. Think of it as "garbage in, garbage out": the error always points back to the source table, not the tool.
This PL-300 practice question tests your understanding of prepare the data. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
During data refresh in Power BI, an error occurs: 'The column 'OrderID' of the table 'Orders' contains a duplicate value and this column is part of a primary key.' The table 'Orders' is imported from an Azure SQL database. What is the most likely cause of this error?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
The 'Orders' table was reordered in Power Query.
Why wrong: Reordering columns doesn't affect data integrity.
Data type mismatch between the source and Power BI.
Why wrong: Data type mismatch would cause a different error.
A calculated column is referencing the 'Orders' table.
Why wrong: Calculated columns don't cause duplicate key errors.
The source table has duplicate 'OrderID' values.
Duplicate values violate the primary key constraint.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The source table has duplicate 'OrderID' values.
Option D is correct because the error message explicitly states that the 'OrderID' column contains a duplicate value and is part of a primary key. In Power BI, when importing from a source like Azure SQL Database, the data model enforces uniqueness on primary key columns. If the source table has duplicate 'OrderID' values, the refresh fails because Power BI cannot maintain the required unique constraint.
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.
The 'Orders' table was reordered in Power Query.
Why it's wrong here
Reordering columns doesn't affect data integrity.
Data type mismatch between the source and Power BI.
Why it's wrong here
Data type mismatch would cause a different error.
A calculated column is referencing the 'Orders' table.
Why it's wrong here
Calculated columns don't cause duplicate key errors.
The source table has duplicate 'OrderID' values.
Why this is correct
Duplicate values violate the primary key constraint.
Clue confirmation
The clue words "most likely", "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates may confuse a primary key violation with other common refresh errors like data type mismatches or query folding issues, but the error message's explicit reference to 'duplicate value' and 'primary key' directly points to source data duplication.
Detailed technical explanation
Under the hood, Power BI uses the M engine to load data and enforces primary key constraints during the refresh process. If the source table has duplicate keys, the engine raises an error because it cannot create a unique index for the relationship. In real-world scenarios, this often occurs when source data is not properly deduplicated or when incremental refresh policies are misconfigured, leading to overlapping key ranges.
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: The source table has duplicate 'OrderID' values. — Option D is correct because the error message explicitly states that the 'OrderID' column contains a duplicate value and is part of a primary key. In Power BI, when importing from a source like Azure SQL Database, the data model enforces uniqueness on primary key columns. If the source table has duplicate 'OrderID' values, the refresh fails because Power BI cannot maintain the required unique constraint.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely", "primary". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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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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