- A
Create a full-text index on email.
Why wrong: Full-text is for text search, not equality.
- B
Create a composite B-tree index on (email, created_at).
This index supports the exact query pattern.
- C
Create a B-tree index on email only.
Why wrong: Does not help range queries on created_at.
- D
Create separate B-tree indexes on email and created_at.
Why wrong: PostgreSQL can use both but may not be as efficient as a composite index.
Question 855 of 1,000
PCDOE Design and Plan Database Solutions Practice Question
This PCDOE practice question tests your understanding of design and plan database solutions. 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 designing a Cloud SQL for PostgreSQL database. The application has a table with 1 million rows that is frequently queried using equality on the 'email' column and range queries on the 'created_at' column. Which index strategy minimizes query latency?
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
✓
Create a composite B-tree index on (email, created_at).
Option B is correct because a composite B-tree index on (email, created_at) allows the database to satisfy both the equality condition on 'email' and the range condition on 'created_at' in a single index scan. PostgreSQL can use the leftmost column for equality filtering and then traverse the index tree to retrieve the range portion efficiently, minimizing random I/O and query latency.
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.
- ✗
Create a full-text index on email.
Why it's wrong here
Full-text is for text search, not equality.
- ✓
Create a composite B-tree index on (email, created_at).
Why this is correct
This index supports the exact query pattern.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a B-tree index on email only.
Why it's wrong here
Does not help range queries on created_at.
- ✗
Create separate B-tree indexes on email and created_at.
Why it's wrong here
PostgreSQL can use both but may not be as efficient as a composite index.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that separate single-column indexes are equivalent to a composite index, but in PostgreSQL, separate indexes require bitmap scans or residual filtering, which are slower than a single composite index that matches the query's equality and range predicates.
Detailed technical explanation
How to think about this question
PostgreSQL's B-tree index stores entries in sorted order; with a composite index on (email, created_at), rows with the same email are stored contiguously in created_at order, enabling a single index range scan. This avoids the overhead of multiple index probes or bitmap heap scans, and the planner can use an Index Only Scan if the index covers the query, reducing heap access. In practice, this pattern is common for user lookup tables where you need to retrieve recent activity for a specific user.
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.
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FAQ
Questions learners often ask
What does this PCDOE question test?
Design and Plan Database Solutions — This question tests Design and Plan Database Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create a composite B-tree index on (email, created_at). — Option B is correct because a composite B-tree index on (email, created_at) allows the database to satisfy both the equality condition on 'email' and the range condition on 'created_at' in a single index scan. PostgreSQL can use the leftmost column for equality filtering and then traverse the index tree to retrieve the range portion efficiently, minimizing random I/O and query latency.
What should I do if I get this PCDOE 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.
About these practice questions
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Last reviewed: Jul 4, 2026
This PCDOE 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 PCDOE exam.
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