Quick Answer
The answer is Left Outer join, because it is the only join kind in Power Query that keeps all rows from the left table—in this case, Orders—while only bringing in matching rows from the right table, Customers. When no match exists on CustomerID, the columns from Customers simply return null values, ensuring no order is lost. On the Microsoft Power BI Data Analyst PL-300 exam, this concept frequently appears in scenario-based questions where you must preserve the primary table’s row count, often testing your ability to distinguish Left Outer from Full Outer (which keeps all rows from both tables) or Inner (which drops non-matching rows). A common trap is confusing Left Outer with Left Anti, which keeps only non-matching rows from the left table. To remember: think of the left table as your “anchor”—it stays intact, and the right table only adds data where it can. A handy mnemonic is “Left Outer: left table always wins, right table fills in the blanks.”
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. The Orders table has a CustomerID column, and the Customers table has a CustomerID column. You want to keep all rows from Orders and only matching rows from Customers. Which join kind should you use?
Full Outer
Why wrong: Full outer join keeps all rows from both tables.
Inner
Why wrong: Inner join only keeps rows that match in both tables.
Left Outer
Left outer join preserves all rows from the left table.
Right Outer
Why wrong: Right outer join preserves all rows from the right table.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Left Outer
Option C (Left Outer) is correct because it returns all rows from the Orders table regardless of whether a matching CustomerID exists in the Customers table. When no match is found, the Customers columns will contain null values. This is the standard behavior for a left outer join in Power Query, which preserves the left table's rows entirely.
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.
Full Outer
Why it's wrong here
Full outer join keeps all rows from both tables.
Inner
Why it's wrong here
Inner join only keeps rows that match in both tables.
Left Outer
Why this is correct
Left outer join preserves all rows from the left table.
Related concept
Read the scenario before looking for a memorised answer.
Right Outer
Why it's wrong here
Right outer join preserves all rows from the right table.
Common exam traps
The trap here is that candidates often confuse Left Outer with Right Outer, mistakenly thinking that 'keeping all rows from Orders' means the Orders table should be on the right side, when in Power Query the join direction is determined by which table is selected as the primary table in the Merge dialog.
Detailed technical explanation
In Power Query, the Left Outer join is implemented by performing a hash-based lookup on the key columns from the right table against the left table. If no match is found, the right table's columns are filled with null values. This join type is particularly useful when you need to enrich a fact table (Orders) with dimension data (Customers) without losing any fact rows, even if some dimension records are missing.
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: Left Outer — Option C (Left Outer) is correct because it returns all rows from the Orders table regardless of whether a matching CustomerID exists in the Customers table. When no match is found, the Customers columns will contain null values. This is the standard behavior for a left outer join in Power Query, which preserves the left table's rows entirely.
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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