The answer is that the DELETE statement processes more bytes than expected because its WHERE clause does not enable BigQuery partition pruning. Even though the condition targets rows older than 100 days, it fails to reference the partitioning column _PARTITIONTIME in a way that allows BigQuery to skip irrelevant partitions. Since the table is partitioned by ingestion time with a 90-day default partition expiration, the DELETE must scan every partition to evaluate the filter, resulting in a full table scan. This scenario tests your understanding of how partition pruning applies to DML operations on the Google Professional Cloud Database Engineer exam—a common trap is assuming that a date-based condition automatically prunes partitions, but BigQuery requires the filter to directly compare the partitioning column. Remember the memory tip: "Prune with the column, not just the value"—always ensure your WHERE clause explicitly references _PARTITIONTIME or _PARTITIONDATE to avoid costly full scans.
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 BigQuery table is partitioned by ingestion time (pseudo column _PARTITIONTIME) and uses the default partition expiration of 90 days. A data engineer runs a DELETE statement to remove rows older than 100 days. Why does this query process more bytes than expected?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The DELETE statement must scan all partitions because it uses a condition that does not prune partitions.
Option D is correct because the DELETE statement uses a condition that does not reference the partitioning column (_PARTITIONTIME) in a way that allows partition pruning. Since the table is partitioned by ingestion time, BigQuery must scan all partitions to evaluate the filter, even though the condition logically targets rows older than 100 days. This results in processing more bytes than expected, as the default partition expiration of 90 days does not reduce the scan scope when the WHERE clause does not leverage the partitioning column.
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.
✗
The table is not partitioned; it is clustered.
Why it's wrong here
The table is partitioned by ingestion time.
✗
The DELETE statement does not use a WHERE clause on a clustering column.
Why it's wrong here
Partition pruning requires a filter on the partition column.
✗
The DELETE statement filters on a custom timestamp column instead of _PARTITIONTIME.
Why it's wrong here
Filtering on a custom column does not enable partition pruning.
✓
The DELETE statement must scan all partitions because it uses a condition that does not prune partitions.
Why this is correct
Without a filter on _PARTITIONTIME or a partition column, the query scans all partitions.
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 misconception that a time-based filter on any timestamp column will trigger partition pruning, when in fact only filters on the specific partitioning column (like _PARTITIONTIME) enable partition elimination.
Detailed technical explanation
How to think about this question
BigQuery uses partition pruning to skip entire partitions when the WHERE clause directly filters on the partitioning column (e.g., _PARTITIONTIME). Without a filter on _PARTITIONTIME, the query must scan all partitions, even if the table has a default partition expiration of 90 days, because the expiration only affects storage, not query processing. In real-world scenarios, this can lead to unexpectedly high costs when engineers assume that time-based filters on other columns will automatically limit the scan to relevant partitions.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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: The DELETE statement must scan all partitions because it uses a condition that does not prune partitions. — Option D is correct because the DELETE statement uses a condition that does not reference the partitioning column (_PARTITIONTIME) in a way that allows partition pruning. Since the table is partitioned by ingestion time, BigQuery must scan all partitions to evaluate the filter, even though the condition logically targets rows older than 100 days. This results in processing more bytes than expected, as the default partition expiration of 90 days does not reduce the scan scope when the WHERE clause does not leverage the partitioning column.
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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