PCDE Practice Question: Define data structures and implement SQL for Business Intelligence
This PCDE practice question tests your understanding of define data structures and implement sql for business intelligence. 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.
A company uses BigQuery for BI reporting. They have a large table 'events' with nested and repeated fields (ARRAY<STRUCT>). Analysts often query unnested data, which is slow. What is the best practice to improve query performance without changing the source schema?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a materialized view that flattens the nested data
Option D is correct because a materialized view in BigQuery can precompute and store the results of an UNNEST operation on nested fields, significantly reducing query time for repeated flattening queries. Unlike a regular view, a materialized view persists the flattened data and is automatically refreshed, so analysts query pre-joined, pre-flattened results without altering the source schema. This directly addresses the performance issue while preserving the original nested structure for other use cases.
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 a view that unnests the data
Why it's wrong here
A view does not precompute; it still incurs the unnest cost each time.
✗
Redesign the table to be flat
Why it's wrong here
Redesign requires changing the pipeline, which may not be feasible.
✗
Use a subquery with UNNEST and cache the results
Why it's wrong here
Caching is temporary and not managed automatically.
✓
Create a materialized view that flattens the nested data
Why this is correct
Materialized views are persisted and automatically refreshed, reducing query time.
Clue confirmation
The clue word "best" 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
Google Cloud often tests the distinction between a view (which is just a saved query) and a materialized view (which physically stores results), leading candidates to mistakenly choose the view option as a quick fix without considering performance implications.
Detailed technical explanation
How to think about this question
BigQuery materialized views use incremental refresh logic to update only changed partitions, leveraging the table's partitioning and clustering to minimize recomputation. Under the hood, the materialized view stores the flattened data as a separate physical table, and BigQuery's query optimizer can automatically rewrite queries to use the materialized view when possible, even if the query does not explicitly reference it. This is especially beneficial for nested fields with high cardinality, where repeated UNNEST operations cause significant shuffle and slot consumption.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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.
Define data structures and implement SQL for Business Intelligence — This question tests Define data structures and implement SQL for Business Intelligence — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a materialized view that flattens the nested data — Option D is correct because a materialized view in BigQuery can precompute and store the results of an UNNEST operation on nested fields, significantly reducing query time for repeated flattening queries. Unlike a regular view, a materialized view persists the flattened data and is automatically refreshed, so analysts query pre-joined, pre-flattened results without altering the source schema. This directly addresses the performance issue while preserving the original nested structure for other use cases.
What should I do if I get this PCDE 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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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