Quick Answer
The answer is GetItem with both ProductId and Category. This is correct because the ProductCatalog table uses a composite primary key where Category serves as the partition key and ProductId as the sort key, and DynamoDB’s GetItem operation provides the most efficient retrieval when you supply both key components, allowing direct access to a single item in exactly one read operation without any scanning or filtering. On the AWS Certified Database Specialty DBS-C01 exam, this tests your understanding of how composite keys enable precise, low-latency lookups, and a common trap is choosing Query with only the partition key, which would return multiple items and require additional filtering. Remember the memory tip: “GetItem needs both keys—partition and sort—for a direct hit, no scan, no sort.”
This DBS-C01 practice question tests your understanding of workload-specific database design. 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 developer sees the above key schema for the ProductCatalog table. Which query will be most efficient for retrieving a single item?
Query with Category = 'Books'
Why wrong: Querying only on sort key is not efficient; it requires a scan.
GetItem with ProductId = '123'
Why wrong: Without the sort key, GetItem cannot uniquely identify an item.
Scan the table and filter by ProductId
Why wrong: Scan reads all items, which is inefficient.
GetItem with ProductId = '123' and Category = 'Books'
Providing both keys uniquely identifies the item.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
GetItem with ProductId = '123' and Category = 'Books'
Option D is correct because the ProductCatalog table's primary key is a composite key of Category (partition key) and ProductId (sort key). A GetItem operation with both the partition key and sort key provides the most efficient direct access to a single item, as it uses the primary key to retrieve the item with exactly one read operation, without any filtering or scanning.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Query with Category = 'Books'
Why it's wrong here
Querying only on sort key is not efficient; it requires a scan.
GetItem with ProductId = '123'
Why it's wrong here
Without the sort key, GetItem cannot uniquely identify an item.
Scan the table and filter by ProductId
Why it's wrong here
Scan reads all items, which is inefficient.
GetItem with ProductId = '123' and Category = 'Books'
Why this is correct
Providing both keys uniquely identifies the item.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often assume GetItem only needs the partition key, forgetting that for tables with a composite primary key (partition key and sort key), both are required to uniquely identify and retrieve a single item.
Detailed technical explanation
In Amazon DynamoDB, the GetItem operation directly accesses an item using its full primary key, achieving O(1) latency by hashing the partition key and then locating the sort key within that partition. This contrasts with Query, which retrieves all items in a partition, and Scan, which reads every partition sequentially. For composite keys, omitting the sort key in GetItem results in a ValidationException because the operation cannot uniquely identify the item without it.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
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FAQ
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..
The correct answer is: GetItem with ProductId = '123' and Category = 'Books' — Option D is correct because the ProductCatalog table's primary key is a composite key of Category (partition key) and ProductId (sort key). A GetItem operation with both the partition key and sort key provides the most efficient direct access to a single item, as it uses the primary key to retrieve the item with exactly one read operation, without any filtering or scanning.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This DBS-C01 practice question is part of Courseiva's free Amazon Web Services 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 DBS-C01 exam.
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