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.
A startup uses Cloud SQL (MySQL) for a blogging platform. The schema has a table 'posts' with columns: post_id (auto-increment PK), title, content, author_id, created_at. The application frequently runs a query to display the latest 10 posts from a specific author: SELECT * FROM posts WHERE author_id = ? ORDER BY created_at DESC LIMIT 10. This query is slow when an author has thousands of posts. The team wants to optimize this query without changing the application code. What schema change will be most effective?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a composite index on (author_id, created_at DESC).
Option A is correct. A composite index on (author_id, created_at) allows the database to efficiently find the posts for a given author ordered by created_at without scanning all rows. Option B (query cache) is not a schema change. Option C (Spanner) is a different database. Option D (partitioning) could help but ordering across partitions is complex and not as effective.
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.
✓
Add a composite index on (author_id, created_at DESC).
Why this is correct
This index directly supports the query, allowing an index range scan and limit.
Related concept
Read the scenario before looking for a memorised answer.
✗
Partition the table by author_id using range partitioning.
Why it's wrong here
Partitioning can help but ordering by created_at across partitions still requires scanning multiple partitions.
✗
Increase the query cache size in Cloud SQL.
Why it's wrong here
Caching is a temporary fix and not a schema design change.
✗
Migrate the posts table to Cloud Spanner and use interleaved indexes.
Why it's wrong here
This is a database migration, not a schema change within Cloud SQL.
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 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 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: Add a composite index on (author_id, created_at DESC). — Option A is correct. A composite index on (author_id, created_at) allows the database to efficiently find the posts for a given author ordered by created_at without scanning all rows. Option B (query cache) is not a schema change. Option C (Spanner) is a different database. Option D (partitioning) could help but ordering across partitions is complex and not as effective.
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.
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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