The answer is to use repeated fields and denormalization as best practices when designing BigQuery schemas. Repeated fields allow you to store nested, parent-child data within a single row, which avoids expensive JOIN operations and dramatically improves query performance in BigQuery’s columnar storage. Denormalization further reduces the need for joins by flattening related data into a single table, aligning with BigQuery’s architecture that charges by the amount of data processed rather than storage. On the Google Professional Cloud Database Engineer exam, this question tests your understanding that schema design in BigQuery prioritizes query speed over traditional normalization rules—a common trap is confusing security features like column-level access with schema design, or assuming a single table is always best. Remember the mnemonic: “Repeated fields reduce row-to-row relations, denormalization dodges joins.”
PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. 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.
Which two of the following are best practices when designing BigQuery schemas? (Choose two.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use denormalization to reduce the number of joins
Options A and C are correct best practices: using repeated fields to avoid joins (common for nested data) and using denormalization to reduce joins. Option B (column-level security) is a security feature, not a schema design best practice. Option D is incorrect because BigQuery encourages logical data models, not a single table. Option E using RECORD is a way to implement nested structures but is not a general best practice by itself; repeated fields are more specific.
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 column-level security to restrict access
Why it's wrong here
Security feature, not specifically a schema design best practice.
✓
Use denormalization to reduce the number of joins
Why this is correct
Denormalization improves query performance by reducing joins.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use the type RECORD for structured data
Why it's wrong here
RECORD is a building block but not a best practice by itself; repeated fields are more impactful.
✓
Use repeated fields to avoid joins when querying parent-child data
Why this is correct
Repeated fields allow storing arrays of records, reducing need for joins.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a single table for all data to simplify queries
Why it's wrong here
Leads to large, complex tables and is not recommended.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which PCDE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Design and implement database schemas — This question tests Design and implement database schemas — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use denormalization to reduce the number of joins — Options A and C are correct best practices: using repeated fields to avoid joins (common for nested data) and using denormalization to reduce joins. Option B (column-level security) is a security feature, not a schema design best practice. Option D is incorrect because BigQuery encourages logical data models, not a single table. Option E using RECORD is a way to implement nested structures but is not a general best practice by itself; repeated fields are more specific.
What should I do if I get this PCDE question wrong?
Identify which PCDE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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