The correct approach is to partition by ingestion time and set expiration on partitions older than 90 days. This works because BigQuery’s partition expiration feature automatically deletes entire partitions once they exceed the specified age, directly reducing storage costs for historical data that is infrequently queried. By using ingestion-time partitioning, you create a clear lifecycle boundary: recent partitions remain for fast BI queries, while older partitions are purged without manual intervention. On the Google Professional Cloud Database Engineer exam, this scenario tests your understanding of cost optimization through data lifecycle management—a common trap is attempting to use table-level expiration or manual deletion, which lacks the granularity and automation of partition expiration. Remember the memory tip: “Partition to purge” — if you partition by time, you can set a timer on each slice, letting BigQuery clean the attic while you keep the living room fast.
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 is using BigQuery for BI and needs to reduce costs for a large historical dataset that is infrequently queried. Which approach should they take?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Partition by ingestion time and set expiration on partitions older than 90 days.
Option C is correct because partitioning by ingestion time allows BigQuery to automatically manage data lifecycle by setting partition expiration. This reduces storage costs for historical data that is infrequently queried, as partitions older than 90 days are deleted without manual intervention. This approach directly addresses the need to reduce costs for a large historical dataset while maintaining query performance on recent data.
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 materialized views for common aggregations.
Why it's wrong here
Materialized views increase storage costs.
✗
Use clustered tables.
Why it's wrong here
Clustering improves query performance but does not reduce storage.
✓
Partition by ingestion time and set expiration on partitions older than 90 days.
Why this is correct
Expired partitions are deleted, reducing storage costs.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a view with a WHERE clause filtering recent data.
Why it's wrong here
Views do not reduce storage; the underlying table remains.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between cost reduction and performance optimization, leading candidates to choose clustering or materialized views (which improve query speed) instead of the storage lifecycle management solution that directly reduces costs.
Detailed technical explanation
How to think about this question
BigQuery partitions by ingestion time use the _PARTITIONTIME pseudo-column, and partition expiration is set at the table level using the `partition_expiration_days` option. When a partition expires, BigQuery deletes all data in that partition, which is a metadata operation that does not require a DELETE statement. This is particularly cost-effective for time-series data like logs or event streams where older data is rarely accessed, as storage costs are the primary driver for large datasets in BigQuery.
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: Partition by ingestion time and set expiration on partitions older than 90 days. — Option C is correct because partitioning by ingestion time allows BigQuery to automatically manage data lifecycle by setting partition expiration. This reduces storage costs for historical data that is infrequently queried, as partitions older than 90 days are deleted without manual intervention. This approach directly addresses the need to reduce costs for a large historical dataset while maintaining query performance on recent data.
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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