The answer is that the query fails because the date format used for the sort key is not lexicographically sortable as a string. DynamoDB’s Query operation with a BETWEEN condition relies on lexicographical order of the sort key string, meaning characters are compared left to right based on their ASCII values. A format like MM-DD-YYYY breaks this order because, for example, “02-15-2024” would sort before “01-20-2025” due to the leading month, whereas YYYY-MM-DD ensures that all dates for a given year group together correctly. On the AWS Certified Data Engineer Associate DEA-01 exam, this concept tests your understanding of how Global Secondary Indexes (GSIs) handle range queries—a common trap is assuming any human-readable date string works, when in fact only ISO 8601 (YYYY-MM-DD) guarantees proper sorting. For a memory tip, remember “Big Endian for Big Queries”: always put the largest time unit first (year, then month, then day) to keep your DynamoDB date queries in order.
DEA-C01 Data Store Management Practice Question
This DEA-C01 practice question tests your understanding of data store management. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Refer to the exhibit. A DynamoDB table 'Orders' has a GSI 'CustomerDateIndex'. A developer tries to query the GSI for all orders of a customer between two dates. The query fails. What is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The query uses a date format that is not lexicographically sortable as a string
Option C is correct because DynamoDB's Query operation requires the sort key to be lexicographically sortable when using comparison operators like BETWEEN. If the 'order_date' attribute is stored as a non-lexicographically sortable string format (e.g., 'MM-DD-YYYY' instead of 'YYYY-MM-DD'), the BETWEEN condition will fail to return correct results or may throw an error. The GSI's sort key must be in a format that supports string comparison for range queries to work properly.
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.
✗
The GSI does not include 'order_id' in the key schema
Why it's wrong here
GSI keys are independent of table keys.
✗
The 'customer_id' attribute is not a partition key in the GSI
Why it's wrong here
It is defined as HASH key.
✓
The query uses a date format that is not lexicographically sortable as a string
Why this is correct
String sort on dates requires ISO 8601 format.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'order_date' attribute is not a sort key in the GSI
Why it's wrong here
It is defined as RANGE key.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that any string date format works for range queries, but the trap here is that DynamoDB requires lexicographically sortable strings for BETWEEN conditions, and non-ISO formats will silently fail or return incorrect results.
Detailed technical explanation
How to think about this question
DynamoDB's Query operation on a GSI uses the partition key for exact equality and the sort key for range queries. For string sort keys, lexicographic ordering is based on ASCII character values, so date formats like '2025-03-15' sort correctly, but '03-15-2025' does not because month comes before year. This is a common pitfall when storing dates as strings; using ISO 8601 format (YYYY-MM-DD) ensures correct range query behavior.
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.
Data Store Management — This question tests Data Store Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The query uses a date format that is not lexicographically sortable as a string — Option C is correct because DynamoDB's Query operation requires the sort key to be lexicographically sortable when using comparison operators like BETWEEN. If the 'order_date' attribute is stored as a non-lexicographically sortable string format (e.g., 'MM-DD-YYYY' instead of 'YYYY-MM-DD'), the BETWEEN condition will fail to return correct results or may throw an error. The GSI's sort key must be in a format that supports string comparison for range queries to work properly.
What should I do if I get this DEA-C01 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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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