Quick Answer
The answer is inner join, because it is the only join kind in Power Query that returns only rows from both tables where there is a match on the join key. When you merge 'Orders' and 'Customers' on CustomerID, an inner join filters out any Orders rows that lack a corresponding CustomerID in the Customers table, keeping only the matching rows. On the Microsoft Power BI Data Analyst PL-300 exam, this concept tests your understanding of table relationships and data shaping in Power Query—a common trap is confusing inner join with left outer join, which would keep all Orders rows even without a match. A reliable memory tip: think of an inner join as a strict handshake—both sides must show up for the row to stay.
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 merging two tables in Power Query: 'Orders' and 'Customers'. You want to include only rows from Orders that have a matching CustomerID in Customers. Which join kind should you use?
Inner join
Returns only matching rows.
Full Outer join
Why wrong: Keeps all rows from both.
Right Outer join
Why wrong: Keeps all rows from Customers.
Left Outer join
Why wrong: Keeps all rows from Orders, not just matches.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Inner join
An inner join in Power Query returns only rows from both tables where there is a match on the join key. Since you want to include only rows from Orders that have a matching CustomerID in Customers, the inner join is the correct choice. It filters out any Orders rows without a corresponding CustomerID in the Customers table.
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.
Inner join
Why this is correct
Returns only matching rows.
Related concept
Read the scenario before looking for a memorised answer.
Full Outer join
Why it's wrong here
Keeps all rows from both.
Right Outer join
Why it's wrong here
Keeps all rows from Customers.
Left Outer join
Why it's wrong here
Keeps all rows from Orders, not just matches.
Common exam traps
The trap here is that candidates often confuse left outer join (which keeps all rows from the first table) with inner join, mistakenly thinking they need to preserve all Orders rows, but the question explicitly requires only matching rows.
Detailed technical explanation
In Power Query, join operations are performed using the Table.Join or Merge Queries dialog, which maps to M language functions like Table.Join with JoinKind.Inner. Under the hood, the engine uses hash-based matching on the key columns for efficiency. A real-world scenario is when you need to analyze only orders that have valid customer records, ensuring data integrity by excluding orphaned orders.
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.
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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: Inner join — An inner join in Power Query returns only rows from both tables where there is a match on the join key. Since you want to include only rows from Orders that have a matching CustomerID in Customers, the inner join is the correct choice. It filters out any Orders rows without a corresponding CustomerID in the Customers table.
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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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. You are merging two queries in Power Query: 'Orders' and 'Customers'. The 'Orders' table has a 'CustomerID' column, and 'Customers' has 'CustomerID' and 'Name'. You need to bring the 'Name' into 'Orders' but only for matching CustomerIDs; unmatched rows should be removed. Which join kind should you use?
hardWhy C: The Inner join kind in Power Query returns only rows where there is a match in both tables based on the key columns. Since the requirement is to bring the 'Name' into 'Orders' only for matching CustomerIDs and to remove unmatched rows, the Inner join is the correct choice. It ensures that only orders with a corresponding customer in the 'Customers' table are retained, and the 'Name' column is added to those matching rows.
Last reviewed: Jun 24, 2026
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