The answer is a misspelled column name, specifically 'SubTotal' instead of 'Subtotal'. This is correct because Power Query M is case-sensitive when referencing column names, so any deviation—even a single capital letter—causes a runtime error as the engine cannot find the non-existent column. On the Microsoft Power BI Data Analyst PL-300 exam, this scenario tests your understanding of M script syntax and common data import pitfalls, often appearing as a trap where a seemingly minor typo breaks an entire query. A useful memory tip is to think of Power Query as "case-crazy": always match the exact casing from the source table, and when in doubt, use the formula bar's auto-complete feature to verify column names.
PL-300 Visualize and analyze the data Practice Question
This PL-300 practice question tests your understanding of visualize and analyze 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.
Exhibit
Refer to the exhibit.
```
let
Source = Sql.Database("server01", "AdventureWorks"),
Sales = Source{[Schema="dbo",Item="SalesOrderHeader"]}[Data],
#"Filtered Rows" = Table.SelectRows(Sales, each [OrderDate] >= #date(2023,1,1) and [OrderDate] < #date(2024,1,1)),
#"Grouped Rows" = Table.Group(#"Filtered Rows", {"CustomerID"}, {{"TotalSales", each List.Sum([SubTotal]), type nullable number}}),
#"Sorted Rows" = Table.Sort(#"Grouped Rows",{{"TotalSales", Order.Descending}}),
#"Top Rows" = Table.FirstN(#"Sorted Rows", 10)
in
#"Top Rows"
```
You are reviewing a Power Query M script that imports sales data. The script filters orders from 2023, groups by CustomerID to sum SubTotal, sorts descending, and takes the top 10 customers. However, the query fails with an error. What is the most likely cause?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The column name 'SubTotal' is misspelled; the correct column name is 'Subtotal'.
Option C is correct because the error is most likely caused by a misspelled column name in the M script. Power Query is case-sensitive for column names, so 'SubTotal' does not match the actual column 'Subtotal', causing a runtime error when the script tries to reference the non-existent column.
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.
✗
The parameters in Sql.Database are reversed; the correct order is database name first, then server.
Why it's wrong here
First parameter is server, second is database; order is correct.
✗
The Table.FirstN function is missing the second argument; it should be Table.FirstN(#"Sorted Rows", 10).
Why it's wrong here
The second argument '10' is present.
✓
The column name 'SubTotal' is misspelled; the correct column name is 'Subtotal'.
Why this is correct
Common typographical error; column names are case-sensitive in some databases.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The #date function cannot be used with a datetime column; use DateTime.From instead.
Why it's wrong here
#date creates a date; comparison with datetime works via implicit conversion.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may overlook case sensitivity in Power Query M and assume column names are case-insensitive like in SQL Server, leading them to dismiss a simple typo as the root cause.
Detailed technical explanation
How to think about this question
Power Query M is case-sensitive for column names, meaning 'SubTotal' and 'Subtotal' are treated as different identifiers. When a column reference does not match exactly, the engine throws an 'Expression.Error: The column 'SubTotal' of the table was not found' error. This is a common pitfall when importing data from sources like SQL Server, where column names may have mixed case but are often referenced inconsistently in M scripts.
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.
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: The column name 'SubTotal' is misspelled; the correct column name is 'Subtotal'. — Option C is correct because the error is most likely caused by a misspelled column name in the M script. Power Query is case-sensitive for column names, so 'SubTotal' does not match the actual column 'Subtotal', causing a runtime error when the script tries to reference the non-existent column.
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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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