DBS-C01 Workload-Specific Database Design Practice Question
Network Topology
A developer sees the above key schema for the ProductCatalog table. Which query will be most efficient for retrieving a single item?
⚠ Common exam trap
Many exam-takers 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.
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
✓
GetItem with ProductId = '123' and Category = 'Books'
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.
Answer analysis
Option-by-option breakdown
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.
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