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 retail company is designing a Cloud Spanner schema for an order management system. Orders are identified by a UUID and contain multiple line items. Each line item references a product. Which schema design best supports high read throughput for queries that retrieve all line items for a given order?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create an Orders table and a LineItems table interleaved in Orders with ORDER_ID as the parent key.
Option B is correct because Cloud Spanner interleaved tables store child rows (LineItems) physically adjacent to their parent row (Orders) on the same split, enabling a single key lookup to retrieve all line items for a given order without cross-table joins or distributed queries. This colocation maximizes read throughput by minimizing latency and avoiding scatter-gather operations across nodes.
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.
✗
Store orders and line items in a single table with repeated fields for line items.
Why it's wrong here
Single table with repeated fields is not supported in Cloud Spanner; also leads to wide rows.
✓
Create an Orders table and a LineItems table interleaved in Orders with ORDER_ID as the parent key.
Why this is correct
Interleaving colocates line items with their order for fast retrieval.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Create separate Orders and LineItems tables with a foreign key relationship and index on ORDER_ID.
Why it's wrong here
Foreign key requires joins and can be slower than interleaving.
✗
Denormalize product information into the LineItems table and store orders separately.
Why it's wrong here
Denormalization increases storage and complexity without performance benefit for this query pattern.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that a foreign key with an index is equivalent to interleaving for performance, but in Cloud Spanner, only interleaved tables guarantee physical colocation and single-split access for parent-child queries, whereas indexed foreign keys still require distributed lookups.
Detailed technical explanation
How to think about this question
Interleaved tables in Cloud Spanner use a hierarchical primary key where the parent key (ORDER_ID) is the prefix of the child key (ORDER_ID, LINE_ITEM_ID), ensuring that all line items for an order are stored contiguously on the same tablet. This design leverages Spanner's distributed storage engine to serve range scans (e.g., WHERE ORDER_ID = ?) with minimal RPCs and no cross-node coordination, which is critical for high-throughput order management systems processing thousands of concurrent queries.
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: Create an Orders table and a LineItems table interleaved in Orders with ORDER_ID as the parent key. — Option B is correct because Cloud Spanner interleaved tables store child rows (LineItems) physically adjacent to their parent row (Orders) on the same split, enabling a single key lookup to retrieve all line items for a given order without cross-table joins or distributed queries. This colocation maximizes read throughput by minimizing latency and avoiding scatter-gather operations across nodes.
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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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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