Quick Answer
The answer is to query the CustomerIndex GSI by CustomerID and OrderDate. This is the most efficient approach because a Global Secondary Index (GSI) allows you to perform targeted lookups using an alternative partition and sort key combination, directly retrieving only the items that match both attributes without scanning the entire base table. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of how GSIs optimize read operations by avoiding expensive full-table scans, a common trap where candidates mistakenly query the base table or use a filter instead of leveraging the index’s sort key. The key insight is that a GSI with a composite sort key like OrderDate enables range queries or precise lookups, drastically reducing consumed read capacity units. Remember the memory tip: “GSI for the key, not the whole table” — always query the index directly when your filter matches its schema.
This DEA-C01 practice question tests your understanding of data store management. 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 data engineer runs this CLI command. Which query is MOST efficient against this table?
Query the CustomerIndex GSI by CustomerID and OrderDate.
The GSI is designed for this query pattern.
Scan the table to find all orders for a CustomerID.
Why wrong: Scan is inefficient compared to using GSI.
Create a local secondary index on CustomerID.
Why wrong: LSI is not shown; GSI exists.
Query by OrderID and filter by OrderDate.
Why wrong: This is efficient but not the most for CustomerID queries.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Query the CustomerIndex GSI by CustomerID and OrderDate.
The CLI command likely created a global secondary index (GSI) named CustomerIndex on CustomerID and OrderDate. Querying this GSI directly is the most efficient because it uses the index's sort key to retrieve only the relevant items without scanning the entire table, minimizing read capacity consumption.
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 the CustomerIndex GSI by CustomerID and OrderDate.
Why this is correct
The GSI is designed for this query pattern.
Related concept
Read the scenario before looking for a memorised answer.
Scan the table to find all orders for a CustomerID.
Why it's wrong here
Scan is inefficient compared to using GSI.
Create a local secondary index on CustomerID.
Why it's wrong here
LSI is not shown; GSI exists.
Query by OrderID and filter by OrderDate.
Why it's wrong here
This is efficient but not the most for CustomerID queries.
Common exam traps
The trap here is that candidates often default to scanning or creating a local secondary index without recognizing that a GSI already exists and is purpose-built for the query pattern, leading to inefficient or invalid solutions.
Trap categories for this question
Command / output trap
LSI is not shown; GSI exists.
Detailed technical explanation
In DynamoDB, a GSI has its own partition and sort keys independent of the base table, allowing efficient querying on non-primary key attributes. When you query a GSI, you specify the partition key (CustomerID) and optionally a sort key condition (OrderDate), and DynamoDB retrieves only the matching items, projecting attributes as defined. This avoids the full table scan and reduces read costs, especially important for large tables with millions of items.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Data Store Management — This question tests Data Store Management — Read the scenario before looking for a memorised answer..
The correct answer is: Query the CustomerIndex GSI by CustomerID and OrderDate. — The CLI command likely created a global secondary index (GSI) named CustomerIndex on CustomerID and OrderDate. Querying this GSI directly is the most efficient because it uses the index's sort key to retrieve only the relevant items without scanning the entire table, minimizing read capacity consumption.
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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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A data engineer runs the describe-table command shown in the exhibit. The application frequently queries by CustomerID alone. Currently, these queries result in full table scans. Which action should the engineer take to improve query performance?
mediumWhy D: The `describe-table` output shows CustomerID is the partition key, but the application frequently queries by CustomerID alone, which currently causes full table scans because there is no index supporting that query pattern. Creating a global secondary index (GSI) on CustomerID allows efficient querying by CustomerID without scanning the entire table, as the GSI provides a separate data structure with its own read/write capacity that can be queried directly.
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Last reviewed: Jun 24, 2026
This DEA-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 DEA-C01 exam.
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