- A
Window function ROW_NUMBER
Why wrong: ROW_NUMBER assigns a sequential number but does not directly count array elements.
- B
UNNEST with COUNT
UNNEST expands the array, then COUNT(*) gives the number of line items per order.
- C
STRUCT with aggregation
Why wrong: STRUCT is for grouping fields, not counting array elements.
- D
ARRAY_LENGTH
ARRAY_LENGTH returns the number of elements in the repeated field directly.
- E
SELECT * EXCEPT
Why wrong: EXCEPT is for excluding columns, not for counting array elements.
Question 168 of 1,000
PDE Ingesting and Processing the Data Practice Question
This PDE practice question tests your understanding of ingesting and processing the data. 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.
You are building a BigQuery table that contains nested and repeated fields (e.g., order with line items). You need to write a query that counts the number of line items per order. Which TWO SQL functions/techniques can you use?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
UNNEST with COUNT
Option B is correct because UNNEST flattens the repeated line items array into individual rows, allowing COUNT to aggregate the number of line items per order. Option D is correct because ARRAY_LENGTH directly returns the number of elements in the repeated field array, which corresponds to the line item count.
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.
- ✗
Window function ROW_NUMBER
Why it's wrong here
ROW_NUMBER assigns a sequential number but does not directly count array elements.
- ✓
UNNEST with COUNT
Why this is correct
UNNEST expands the array, then COUNT(*) gives the number of line items per order.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
STRUCT with aggregation
Why it's wrong here
STRUCT is for grouping fields, not counting array elements.
- ✓
ARRAY_LENGTH
Why this is correct
ARRAY_LENGTH returns the number of elements in the repeated field directly.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
SELECT * EXCEPT
Why it's wrong here
EXCEPT is for excluding columns, not for counting array elements.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between functions that operate on arrays directly (like ARRAY_LENGTH) versus those that require row-level expansion (like UNNEST), and candidates may mistakenly choose window functions or STRUCT-based aggregation that do not directly count array elements.
Detailed technical explanation
How to think about this question
In BigQuery, repeated fields are stored as arrays, and ARRAY_LENGTH returns the cardinality of the array without requiring a JOIN or UNNEST. UNNEST with COUNT works by laterally exploding the array into rows, then aggregating; this is useful when you need to filter or join on individual array elements before counting. A subtle behavior: ARRAY_LENGTH counts NULL elements as part of the array length, while UNNEST with COUNT will exclude NULLs unless you explicitly handle them.
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.
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FAQ
Questions learners often ask
What does this PDE question test?
Ingesting and Processing the Data — This question tests Ingesting and Processing the Data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: UNNEST with COUNT — Option B is correct because UNNEST flattens the repeated line items array into individual rows, allowing COUNT to aggregate the number of line items per order. Option D is correct because ARRAY_LENGTH directly returns the number of elements in the repeated field array, which corresponds to the line item count.
What should I do if I get this PDE 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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Last reviewed: Jul 4, 2026
This PDE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PDE exam.
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