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 company is migrating a large Oracle database to Cloud Spanner. The schema includes several tables with foreign key relationships. The team wants to minimize query latency for join queries that always involve a parent table and its children. Which THREE schema design strategies should the team consider? (Choose THREE.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Design child table primary keys to start with the parent key (e.g., CustomerId, OrderId)
Option A is correct because in Cloud Spanner, designing child table primary keys to start with the parent key (e.g., CustomerId, OrderId) enables efficient key-range scans and reduces the number of splits needed for join queries. This pattern leverages Spanner's distributed architecture to colocate related rows, minimizing cross-node communication 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.
✓
Design child table primary keys to start with the parent key (e.g., CustomerId, OrderId)
Why this is correct
Enables interleaving and efficient queries.
Clue confirmation
The clue words "always", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
Denormalize frequently joined lookup tables into the parent table as repeated fields
Why this is correct
Reduces the need for joins.
Clue confirmation
The clue words "always", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✓
Use parent-child interleaved tables where the child table's primary key includes the parent's primary key
Why this is correct
Co-locates rows for efficient joins.
Clue confirmation
The clue words "always", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create secondary indexes on foreign key columns
Why it's wrong here
Secondary indexes do not co-locate data; joins still require distributed reads.
✗
Store foreign key relationships as JSON arrays in the parent table
Why it's wrong here
Violates normalization and complicates queries; not recommended.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that secondary indexes alone can optimize join performance in distributed databases, but in Spanner, physical colocation via interleaved tables is the key to minimizing query latency for parent-child joins.
Detailed technical explanation
How to think about this question
Cloud Spanner uses interleaved tables to physically store child rows adjacent to their parent row within the same split, enabling zero-hop joins for queries that filter on the parent key. This design is analogous to index-organized tables in Oracle but is implemented at the schema level in Spanner, requiring the child table's primary key to include the parent key as a prefix. In real-world scenarios, this pattern is essential for high-throughput transactional workloads like order management systems, where parent-child joins are frequent and latency-sensitive.
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.
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: Design child table primary keys to start with the parent key (e.g., CustomerId, OrderId) — Option A is correct because in Cloud Spanner, designing child table primary keys to start with the parent key (e.g., CustomerId, OrderId) enables efficient key-range scans and reduces the number of splits needed for join queries. This pattern leverages Spanner's distributed architecture to colocate related rows, minimizing cross-node communication and query latency.
What should I do if I get this PCDE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "always", "minimum / minimize". Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.
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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