The answer is that the timestamp field is not defined as a partition column in the Glue table. This is the most likely cause because Athena relies on partition pruning to efficiently filter data; when a time-range filter is applied to a column that is not a partition key, Athena must scan every file in the table, but if the data is physically organized by partitions (e.g., year/month/day folders) and the Glue catalog does not reflect that structure, the query will return zero results for filtered time ranges. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this question tests your understanding of how Glue crawlers and Athena interact with partitioned S3 data—a common trap is assuming Athena can automatically infer partitions from a timestamp field within the data itself, when in fact partitions must be explicitly defined in the table schema. Remember the memory tip: “Partitions are paths, not fields”—the partition column must mirror the S3 folder structure, not just a JSON key.
MLS-C01 Data Engineering Practice Question
This MLS-C01 practice question tests your understanding of data engineering. 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.
A data scientist is building a training dataset from data stored in Amazon S3. The data consists of JSON files each containing a 'timestamp' field. The scientist wants to use AWS Glue to catalog the data and enable querying via Amazon Athena. However, Athena queries are returning zero results for time-range filters. What is the most likely cause?
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.
The AWS Glue crawler does not have permissions to read the S3 bucket.
Why wrong: Incorrect: If the crawler could not read, the table would not be created.
B
Athena cannot query nested JSON objects.
Why wrong: Incorrect: Athena supports nested JSON using dot notation.
C
The JSON files are not in the correct format for Athena.
Why wrong: Incorrect: Athena supports JSON files.
D
The 'timestamp' field is not defined as a partition column in the Glue table.
Correct: Without partitioning, Athena scans all data, but time-range filters still work; however, the question implies zero results, which could be due to incorrect partition pruning.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'timestamp' field is not defined as a partition column in the Glue table.
Athena uses the partition columns derived from the Glue catalog. If the timestamp column is not used as a partition key, queries that filter on it will scan all data. Option B (timestamp is not a partition column) is correct because Glue can automatically partition by date, but the user must set it. Option A (wrong file format) is unlikely if JSON is supported. Option C (Athena cannot query nested JSON) is false; Athena supports JSON. Option D (insufficient permissions) would cause a different error.
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 AWS Glue crawler does not have permissions to read the S3 bucket.
Why it's wrong here
Incorrect: If the crawler could not read, the table would not be created.
✗
Athena cannot query nested JSON objects.
Why it's wrong here
Incorrect: Athena supports nested JSON using dot notation.
✗
The JSON files are not in the correct format for Athena.
The 'timestamp' field is not defined as a partition column in the Glue table.
Why this is correct
Correct: Without partitioning, Athena scans all data, but time-range filters still work; however, the question implies zero results, which could be due to incorrect partition pruning.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which MLS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Data Engineering — This question tests Data Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The 'timestamp' field is not defined as a partition column in the Glue table. — Athena uses the partition columns derived from the Glue catalog. If the timestamp column is not used as a partition key, queries that filter on it will scan all data. Option B (timestamp is not a partition column) is correct because Glue can automatically partition by date, but the user must set it. Option A (wrong file format) is unlikely if JSON is supported. Option C (Athena cannot query nested JSON) is false; Athena supports JSON. Option D (insufficient permissions) would cause a different error.
What should I do if I get this MLS-C01 question wrong?
Identify which MLS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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