PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. 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
SELECT country, SUM(sales)
FROM sales_data
WHERE date BETWEEN '2023-01-01' AND '2023-01-31'
GROUP BY country
-- Query results: bytes processed: 500 GB, bytes billed: 500 GB, number of partitions processed: 31
Refer to the exhibit. You receive the following query output showing bytes processed for a BigQuery query. The table is partitioned by date and clustered on country. What is the most likely reason for the high bytes processed?
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.
SELECT country, SUM(sales)
FROM sales_data
WHERE date BETWEEN '2023-01-01' AND '2023-01-31'
GROUP BY country
-- Query results: bytes processed: 500 GB, bytes billed: 500 GB, number of partitions processed: 31
A
The GROUP BY country requires sorting all rows
Why wrong: Sorting is a factor but not the primary reason for high bytes processed.
B
The table is not partitioned correctly
Why wrong: The query processed exactly 31 partitions, meaning partitioning is effective.
C
The date range is too wide
Why wrong: 31 days is a small range; the high bytes suggest scanning all data in those partitions.
D
The query does not filter on the clustering column, causing full scan of selected partitions
Clustering on country helps only if the WHERE clause filters on country; otherwise, all rows in partitions are scanned.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The query does not filter on the clustering column, causing full scan of selected partitions
Option B is correct: the query does not filter on the clustering column (country), so BigQuery must scan all rows in the selected partitions. Clustering only reduces data scanned when there is a filter on the clustering key or when the query aggregates after filtering on it. Option A is incorrect because partitioning is working. Option C is incorrect because 31 days is a small range. Option D is incorrect because the GROUP BY does not cause full scan; the issue is lack of clustering filter.
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 GROUP BY country requires sorting all rows
Why it's wrong here
Sorting is a factor but not the primary reason for high bytes processed.
✗
The table is not partitioned correctly
Why it's wrong here
The query processed exactly 31 partitions, meaning partitioning is effective.
✗
The date range is too wide
Why it's wrong here
31 days is a small range; the high bytes suggest scanning all data in those partitions.
✓
The query does not filter on the clustering column, causing full scan of selected partitions
Why this is correct
Clustering on country helps only if the WHERE clause filters on country; otherwise, all rows in partitions are scanned.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 PCDE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Design and implement database schemas — This question tests Design and implement database schemas — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The query does not filter on the clustering column, causing full scan of selected partitions — Option B is correct: the query does not filter on the clustering column (country), so BigQuery must scan all rows in the selected partitions. Clustering only reduces data scanned when there is a filter on the clustering key or when the query aggregates after filtering on it. Option A is incorrect because partitioning is working. Option C is incorrect because 31 days is a small range. Option D is incorrect because the GROUP BY does not cause full scan; the issue is lack of clustering filter.
What should I do if I get this PCDE question wrong?
Identify which PCDE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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Question Discussion
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