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.
Exhibit
Refer to the exhibit.
```
M query:
let
Source = Sql.Database("myserver.database.windows.net", "SalesDB"),
SalesTable = Source{[Schema="dbo",Item="Sales"]}[Data],
FilteredRows = Table.SelectRows(SalesTable, each [OrderDate] >= #date(2023,1,1)),
GroupedRows = Table.Group(FilteredRows, {"ProductID"}, {{"TotalSales", each List.Sum([Amount]), type number}})
in
GroupedRows
```
You are troubleshooting a Power Query transformation that groups sales data by ProductID. The query runs slowly and you suspect the filter is being applied after loading all rows. What change would improve performance by pushing the filter to the source?
Refer to the exhibit.
```
M query:
let
Source = Sql.Database("myserver.database.windows.net", "SalesDB"),
SalesTable = Source{[Schema="dbo",Item="Sales"]}[Data],
FilteredRows = Table.SelectRows(SalesTable, each [OrderDate] >= #date(2023,1,1)),
GroupedRows = Table.Group(FilteredRows, {"ProductID"}, {{"TotalSales", each List.Sum([Amount]), type number}})
in
GroupedRows
```
A
Disable the 'Enable load' option for the SalesTable
Why wrong: Disabling load would not load any data, which is not desired.
B
Use CALCULATE in DAX to filter
Why wrong: DAX is not used in Power Query; it's for measures.
C
Add a 'Table.Buffer' step after the filter
Why wrong: Buffer does not push filter to source; it caches after loading.
D
Replace the first three lines with a native SQL query that includes the WHERE clause
Native SQL query allows the database to apply the filter before returning data.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Replace the first three lines with a native SQL query that includes the WHERE clause
Option D is correct because pushing filter logic to the source database via a native SQL query with a WHERE clause reduces the amount of data loaded into Power Query. This leverages query folding, which allows the source (e.g., SQL Server) to perform the filtering before data is transferred, significantly improving performance for large datasets.
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.
✗
Disable the 'Enable load' option for the SalesTable
Why it's wrong here
Disabling load would not load any data, which is not desired.
✗
Use CALCULATE in DAX to filter
Why it's wrong here
DAX is not used in Power Query; it's for measures.
✗
Add a 'Table.Buffer' step after the filter
Why it's wrong here
Buffer does not push filter to source; it caches after loading.
✓
Replace the first three lines with a native SQL query that includes the WHERE clause
Why this is correct
Native SQL query allows the database to apply the filter before returning data.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse in-memory buffering (Table.Buffer) or DAX filter functions with source-level query pushdown, failing to recognize that only native SQL or folding-compatible M steps can reduce data transfer from the source.
Detailed technical explanation
How to think about this question
Query folding is the mechanism by which Power Query translates M expressions into source-native queries (e.g., SQL WHERE clauses). When folding is broken (e.g., by using unsupported transformations), Power Query must load all rows into its engine before applying filters, causing performance degradation. In real-world scenarios, using a native SQL query with a WHERE clause ensures folding is explicit and bypasses any folding blockers, especially when dealing with complex transformations that might otherwise prevent automatic folding.
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: Replace the first three lines with a native SQL query that includes the WHERE clause — Option D is correct because pushing filter logic to the source database via a native SQL query with a WHERE clause reduces the amount of data loaded into Power Query. This leverages query folding, which allows the source (e.g., SQL Server) to perform the filtering before data is transferred, significantly improving performance for large datasets.
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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