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 data analyst runs a query joining several large tables and gets 'Resources exceeded' error. They need to reduce memory usage without changing the query logic. What should they do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a subquery to pre-aggregate the largest table before joining
Option A is correct because pre-aggregating the largest table in a subquery reduces the amount of data that needs to be shuffled and joined in memory. In BigQuery, this minimizes the bytes processed and the memory footprint of the join operation, directly addressing the 'Resources exceeded' error without altering the overall query logic.
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 subquery to pre-aggregate the largest table before joining
Why this is correct
Pre-aggregation reduces the row count and columns, decreasing shuffle and memory.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use APPROX_COUNT_DISTINCT for counting distinct values
Why it's wrong here
This only helps with distinct count approximations, not join memory.
✗
Increase the slot reservation
Why it's wrong here
Adding slots can speed up but does not reduce memory per node; the query may still exceed memory limits.
✗
Use SELECT * in the subquery to ensure all columns are available
Why it's wrong here
SELECT * increases data volume, worsening memory issues.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse increasing resources (slots) with reducing memory usage, or they think that approximate functions like APPROX_COUNT_DISTINCT can fix join memory errors, when in fact they only affect aggregation accuracy.
Detailed technical explanation
How to think about this question
In BigQuery, joins are executed using a hash-based shuffle algorithm that distributes rows across worker nodes based on join keys. Pre-aggregation reduces the number of rows and the size of the hash tables, which are the primary memory consumers. A real-world scenario is joining a fact table with billions of rows to a dimension table; pre-aggregating the fact table by the join key and relevant measures can reduce the shuffle data by orders of magnitude.
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: Use a subquery to pre-aggregate the largest table before joining — Option A is correct because pre-aggregating the largest table in a subquery reduces the amount of data that needs to be shuffled and joined in memory. In BigQuery, this minimizes the bytes processed and the memory footprint of the join operation, directly addressing the 'Resources exceeded' error without altering the overall query logic.
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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