- A
Use a composite primary key to include those columns
Why wrong: Changing the primary key is not always feasible and may not be appropriate.
- B
Use the STORING clause to include the queried columns in the index
STORING stores extra columns in the index, avoiding back join.
- C
Use a local secondary index instead of a global one
Why wrong: Local vs global affects distribution but does not store additional columns.
- D
Use interleaving with the base table
Why wrong: Interleaving is for parent-child relationships, not for index optimization.
Question 741 of 999
PCD Practice Question: Design Scalable and Highly Available Cloud Database Solutions
This PCD practice question tests your understanding of design scalable and highly available cloud 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 have a Cloud Spanner database with a table that has a secondary index. You notice that queries using the index are performing a back join to the base table. Which index feature can you use to avoid this back join?
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
✓
Use the STORING clause to include the queried columns in the index
In Cloud Spanner, a secondary index does not store all columns of the base table by default. When a query uses the index but needs columns not present in the index, Spanner performs a back join (also called a table lookup) to retrieve those missing columns from the base table. The STORING clause allows you to include additional non-key columns in the index itself, making the index covering and eliminating the need for the back join.
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 a composite primary key to include those columns
Why it's wrong here
Changing the primary key is not always feasible and may not be appropriate.
- ✓
Use the STORING clause to include the queried columns in the index
Why this is correct
STORING stores extra columns in the index, avoiding back join.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a local secondary index instead of a global one
Why it's wrong here
Local vs global affects distribution but does not store additional columns.
- ✗
Use interleaving with the base table
Why it's wrong here
Interleaving is for parent-child relationships, not for index optimization.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common misconception in Spanner is that a composite primary key or interleaving can substitute for a covering index, but only the STORING clause directly eliminates the need for a back join by storing additional columns in the index.
Detailed technical explanation
How to think about this question
The STORING clause in Cloud Spanner is analogous to INCLUDE columns in other databases (e.g., SQL Server's INCLUDE or PostgreSQL's INCLUDE in unique indexes). When you add a column to the STORING clause, Spanner physically stores that column's value in the index's data blocks, making the index covering for queries that only reference those stored columns. This avoids the extra round-trip to the base table, which is especially beneficial for latency-sensitive applications or high-throughput workloads where every millisecond counts.
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 PCD question test?
Design Scalable and Highly Available Cloud Database Solutions — This question tests Design Scalable and Highly Available Cloud Database Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use the STORING clause to include the queried columns in the index — In Cloud Spanner, a secondary index does not store all columns of the base table by default. When a query uses the index but needs columns not present in the index, Spanner performs a back join (also called a table lookup) to retrieve those missing columns from the base table. The STORING clause allows you to include additional non-key columns in the index itself, making the index covering and eliminating the need for the back join.
What should I do if I get this PCD 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
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