- A
Maintain the same schema and rewrite joins as materialized views in PostgreSQL to optimize queries.
Why wrong: Rewriting joins as views does not address schema compatibility; the application still needs to handle composite keys.
- B
Use the same composite primary keys and foreign key constraints in Cloud SQL for PostgreSQL, leveraging its full support for these features.
Cloud SQL for PostgreSQL fully supports composite primary keys and foreign keys, minimizing application changes.
- C
Migrate to Cloud Spanner instead, using interleaved tables to replace join-heavy operations.
Why wrong: Cloud Spanner would require significant application changes and is not a direct migration path from MySQL.
- D
Remove composite primary keys and replace them with surrogate keys; use look-up tables for foreign key relationships.
Why wrong: This would require extensive application code changes to adapt to new key structures.
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 legacy on-premises MySQL database to Cloud SQL for PostgreSQL. The database uses composite primary keys on multiple tables and heavily relies on cross-table joins with foreign keys. The team wants to minimize application code changes during migration. Which schema design strategy should the Cloud Database Engineer recommend to ensure compatibility and performance?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"primary"Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
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 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 same composite primary keys and foreign key constraints in Cloud SQL for PostgreSQL, leveraging its full support for these features.
Option B is correct because Cloud SQL for PostgreSQL fully supports composite primary keys and foreign key constraints, which are standard SQL features. By maintaining the same schema, the team minimizes application code changes while preserving referential integrity and join performance, as PostgreSQL's query planner handles these constructs efficiently.
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.
- ✗
Maintain the same schema and rewrite joins as materialized views in PostgreSQL to optimize queries.
Why it's wrong here
Rewriting joins as views does not address schema compatibility; the application still needs to handle composite keys.
- ✓
Use the same composite primary keys and foreign key constraints in Cloud SQL for PostgreSQL, leveraging its full support for these features.
Why this is correct
Cloud SQL for PostgreSQL fully supports composite primary keys and foreign keys, minimizing application changes.
Clue confirmation
The clue words "primary", "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Migrate to Cloud Spanner instead, using interleaved tables to replace join-heavy operations.
Why it's wrong here
Cloud Spanner would require significant application changes and is not a direct migration path from MySQL.
- ✗
Remove composite primary keys and replace them with surrogate keys; use look-up tables for foreign key relationships.
Why it's wrong here
This would require extensive application code changes to adapt to new key structures.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume cloud-native databases require schema redesign (e.g., denormalization or surrogate keys) for performance, but PostgreSQL's full SQL compliance often allows a direct lift-and-shift of composite keys and foreign keys without changes.
Detailed technical explanation
How to think about this question
PostgreSQL's query planner can efficiently handle joins on composite foreign keys using hash or merge joins, especially when statistics are up-to-date and appropriate indexes exist. In a real-world migration, the team should also consider using PostgreSQL's `pgloader` tool to automate schema and data migration while preserving constraints, and test query performance with `EXPLAIN ANALYZE` to identify any need for index tuning.
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.
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FAQ
Questions learners often ask
What does this PCDE question test?
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 the same composite primary keys and foreign key constraints in Cloud SQL for PostgreSQL, leveraging its full support for these features. — Option B is correct because Cloud SQL for PostgreSQL fully supports composite primary keys and foreign key constraints, which are standard SQL features. By maintaining the same schema, the team minimizes application code changes while preserving referential integrity and join performance, as PostgreSQL's query planner handles these constructs efficiently.
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: "primary", "minimum / minimize". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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