The correct DAX measure is Net Sales = SUMX(Sales, Sales[SalesAmount] * (1 - COALESCE(Sales[Discount], 0))). This is correct because it uses SUMX to perform a row-by-row iteration over the Sales table, applying the net sales calculation individually to each row, while COALESCE replaces any NULL discount with zero, ensuring the formula handles null discount values without breaking the arithmetic. On the PL-300 exam, this tests your understanding of row context versus aggregation context, and the common trap is using SUM(Sales[Discount]) directly, which would either ignore NULLs or produce incorrect totals. The key insight is that COALESCE is the modern replacement for IF(ISBLANK()) in DAX, and it works seamlessly inside iterators like SUMX. Memory tip: think "COALESCE to coerce NULLs to zero" — it turns missing discounts into a clean zero for safe multiplication.
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.
Network Topology
Refer to the exhibit. You load the Sales table into Power BI. You need to calculate the total net sales after discount (SalesAmount * (1 - Discount)). However, some rows have Null in the Discount column. What is the correct DAX measure?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Net Sales = SUMX(Sales, Sales[SalesAmount] * (1 - COALESCE(Sales[Discount], 0)))
Option B is correct because it uses SUMX to iterate over each row of the Sales table, applying the calculation row-by-row, and uses COALESCE to replace any NULL in the Discount column with 0, ensuring the discount is correctly treated as zero for rows without a discount. This avoids the aggregation errors that occur when using SUM on the Discount column directly.
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.
✗
Net Sales = SUM(Sales[SalesAmount]) * (1 - SUM(Sales[Discount]))
Why it's wrong here
This incorrectly sums discounts first.
✓
Net Sales = SUMX(Sales, Sales[SalesAmount] * (1 - COALESCE(Sales[Discount], 0)))
Why this is correct
COALESCE replaces Null with 0.
Related concept
Read the scenario before looking for a memorised answer.
✗
Net Sales = SUMX(Sales, Sales[SalesAmount] * (1 - Sales[Discount]))
Why it's wrong here
Null in Discount makes the whole expression Null.
✗
Net Sales = SUMX(Sales, DIVIDE(Sales[SalesAmount], 1 - Sales[Discount]))
Why it's wrong here
DIVIDE with Null divisor returns an error or blank.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose Option C, thinking that DAX will automatically ignore NULLs in multiplication, when in fact any NULL operand produces a NULL result, leading to incorrect totals.
Detailed technical explanation
How to think about this question
Under the hood, SUMX is an iterator that evaluates an expression for each row of the specified table, then sums the results. COALESCE (or its older equivalent IF(ISBLANK(...), 0, ...)) is essential in DAX to convert NULLs to a neutral value (0) before arithmetic, because any arithmetic operation involving NULL yields NULL. In real-world scenarios, discount columns often have missing values for items sold at full price, and failing to handle these NULLs would silently drop entire rows from the total.
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: Net Sales = SUMX(Sales, Sales[SalesAmount] * (1 - COALESCE(Sales[Discount], 0))) — Option B is correct because it uses SUMX to iterate over each row of the Sales table, applying the calculation row-by-row, and uses COALESCE to replace any NULL in the Discount column with 0, ensuring the discount is correctly treated as zero for rows without a discount. This avoids the aggregation errors that occur when using SUM on the Discount column directly.
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.
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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