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 stores user events in BigQuery as nested repeated fields. They want to use Looker to build dashboards on individual events. Which SQL pattern should they use in a derived table to flatten the data?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SELECT fields FROM table, UNNEST(events) AS event
Option B is correct because UNNEST(events) in BigQuery SQL flattens the nested repeated field 'events' into individual rows, enabling Looker to treat each event as a separate record for dashboarding. This is the standard pattern for denormalizing arrays in BigQuery derived tables, as it converts each array element into its own row while preserving the parent record's fields.
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.
✗
SELECT fields FROM table WHERE events IS NOT NULL
Why it's wrong here
This does not flatten the array; it just filters rows.
✓
SELECT fields FROM table, UNNEST(events) AS event
Why this is correct
CROSS JOIN UNNEST flattens the events array into rows, allowing access to event fields.
Related concept
Read the scenario before looking for a memorised answer.
✗
SELECT ARRAY_AGG(events) FROM table
Why it's wrong here
ARRAY_AGG aggregates rows into an array, the opposite of flattening.
✗
SELECT events.* FROM table
Why it's wrong here
This attempts to select fields from the array without unnesting, which is invalid.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that simply selecting the nested field (option D) or filtering it (option A) will flatten the data, when in fact only UNNEST (or explicit CROSS JOIN UNNEST) achieves row-level expansion in BigQuery SQL.
Detailed technical explanation
How to think about this question
Under the hood, BigQuery stores nested repeated fields as arrays of STRUCTs; UNNEST performs a lateral cross join that expands each array element into a separate row, effectively creating a one-to-many relationship from the parent row. A subtle behavior is that UNNEST can be used with CROSS JOIN or in the FROM clause with a comma, and it automatically handles NULL arrays by excluding them unless LEFT JOIN is used. In real-world scenarios, this pattern is critical for event analytics (e.g., user session events) where each event must be aggregated or filtered independently in Looker.
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: SELECT fields FROM table, UNNEST(events) AS event — Option B is correct because UNNEST(events) in BigQuery SQL flattens the nested repeated field 'events' into individual rows, enabling Looker to treat each event as a separate record for dashboarding. This is the standard pattern for denormalizing arrays in BigQuery derived tables, as it converts each array element into its own row while preserving the parent record's fields.
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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