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.
A company has a BigQuery table partitioned by ingestion time. They want to create a BI report showing month-over-month revenue growth. To minimize query cost, what should they do?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a WHERE clause with _PARTITIONDATE >= DATE_SUB(CURRENT_DATE(), INTERVAL 13 MONTH) and LAG
Option A is correct because it uses a WHERE clause with _PARTITIONDATE >= DATE_SUB(CURRENT_DATE(), INTERVAL 13 MONTH) to prune partitions, ensuring BigQuery scans only the necessary 13 months of data. The LAG function then computes month-over-month revenue growth efficiently. This minimizes query cost by reducing the amount of data processed, which is critical for ingestion-time partitioned tables.
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.
✓
Use a WHERE clause with _PARTITIONDATE >= DATE_SUB(CURRENT_DATE(), INTERVAL 13 MONTH) and LAG
Why this is correct
This filters to only the necessary partitions for the last 13 months (to compute month-over-month) and uses LAG for growth.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use DATE_TRUNC on the ingestion timestamp without filtering partitions
Why it's wrong here
Without partition filter, the query scans all partitions, increasing cost.
✗
Use LAG without a partition filter
Why it's wrong here
LAG alone does not filter partitions; still scans all data.
✗
Use a wildcard table with UNION ALL over monthly tables
Why it's wrong here
Wildcard tables may scan all tables if not filtered, and are less efficient than partitioning.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that any date function or window function alone reduces cost, but without explicit partition pruning (e.g., _PARTITIONDATE filter), BigQuery still scans all partitions, negating cost benefits.
Detailed technical explanation
How to think about this question
Ingestion-time partitioned tables in BigQuery use a hidden _PARTITIONDATE pseudo-column that reflects the UTC date of ingestion. By filtering on _PARTITIONDATE, BigQuery performs partition pruning at the storage layer, scanning only the relevant columnar data blocks. The LAG window function, when used with a proper ORDER BY clause over a date column, computes the previous month's revenue without requiring a self-join, making the query both cost-effective and performant.
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 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 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: Use a WHERE clause with _PARTITIONDATE >= DATE_SUB(CURRENT_DATE(), INTERVAL 13 MONTH) and LAG — Option A is correct because it uses a WHERE clause with _PARTITIONDATE >= DATE_SUB(CURRENT_DATE(), INTERVAL 13 MONTH) to prune partitions, ensuring BigQuery scans only the necessary 13 months of data. The LAG function then computes month-over-month revenue growth efficiently. This minimizes query cost by reducing the amount of data processed, which is critical for ingestion-time partitioned tables.
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: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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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