PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. 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.
A data warehouse in BigQuery stores daily snapshots of customer data. The schema uses a single table with a snapshot_date partition column. Over time, the table has grown to 10 TB and queries often scan entire partitions. Which schema redesign would improve query performance and reduce costs significantly?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a nested and repeated structure to store all snapshots per customer in a single row.
Using nested and repeated fields (Option D) to store all snapshots per customer in a single row drastically reduces data scanned when querying by customer. Option A (clustering) still scans full partitions if querying across dates. Options B and C (separate tables/wildcards) still require scanning multiple partitions.
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.
✗
Create separate tables for each snapshot_date.
Why it's wrong here
This increases management overhead and does not reduce per-query bytes scanned.
✗
Use clustering on customer_id and snapshot_date.
Why it's wrong here
Clustering helps but queries that scan many dates still process large amounts of data.
✓
Use a nested and repeated structure to store all snapshots per customer in a single row.
Why this is correct
Nested fields allow storing an array of snapshots per customer, reducing data scanned per query significantly.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a wildcard table with a _TABLE_SUFFIX filter.
Why it's wrong here
Same as B, still need to scan multiple tables if querying multiple dates.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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: Use a nested and repeated structure to store all snapshots per customer in a single row. — Using nested and repeated fields (Option D) to store all snapshots per customer in a single row drastically reduces data scanned when querying by customer. Option A (clustering) still scans full partitions if querying across dates. Options B and C (separate tables/wildcards) still require scanning multiple partitions.
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.
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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