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. 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.
Which TWO of the following are valid ways to improve the performance of a BigQuery query that joins two large tables?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Apply WHERE clauses to filter each table before the join.
Option A is correct because applying WHERE clauses before the join (e.g., using subqueries or CTEs to pre-filter each table) reduces the amount of data shuffled and processed during the join phase. BigQuery's query engine can push down filters to the storage layer, minimizing the bytes read and improving performance significantly.
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.
✓
Apply WHERE clauses to filter each table before the join.
Why this is correct
Reducing data before joining improves performance.
Related concept
Read the scenario before looking for a memorised answer.
✓
Create a materialized view that pre-joins the tables.
Read the scenario before looking for a memorised answer.
✗
Use the 'JOIN EACH' clause.
Why it's wrong here
JOIN EACH is not a valid BigQuery syntax for improving join performance.
✗
Denormalize the tables into a single table.
Why it's wrong here
Denormalization is a schema change, not a query optimization technique for a given schema.
✗
Set the query option 'USE_CACHE=TRUE'.
Why it's wrong here
Caching caches query results, not join processing.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that 'JOIN EACH' is still required for large joins, when in fact it is a deprecated syntax and modern BigQuery handles large joins automatically without any special clause.
Detailed technical explanation
How to think about this question
BigQuery uses a columnar storage format (Capacitor) and a distributed shuffle architecture. Pre-filtering reduces the number of rows entering the shuffle phase, which is often the bottleneck in large joins. Materialized views (Option B) are pre-computed and incrementally refreshed, allowing BigQuery to rewrite queries to use the view instead of scanning the base tables, which can dramatically reduce query cost and latency for repeated join patterns.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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: Apply WHERE clauses to filter each table before the join. — Option A is correct because applying WHERE clauses before the join (e.g., using subqueries or CTEs to pre-filter each table) reduces the amount of data shuffled and processed during the join phase. BigQuery's query engine can push down filters to the storage layer, minimizing the bytes read and improving performance significantly.
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.
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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