MLS-C01 Athena data types Practice Question
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?
⚠ Common exam trap
Candidates may assume that time-range filter failures are always due to missing partition columns, but often the issue is with the data format or timestamp parsing.
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
✓
The JSON files are not in the correct format for Athena.
Athena supports querying JSON data, but the JSON files must have a schema that Athena can interpret. If the 'timestamp' field is in an unrecognized date/time format or the JSON structure is inconsistent, Athena may fail to parse the data correctly, resulting in zero rows for time-range filters. Option C is correct because the most likely cause is the JSON files not being in a format that Athena can parse properly for timestamp filtering. Option A is wrong because permission issues would cause an access denied error. Option B is wrong because Athena supports nested JSON. Option D is wrong because even if the timestamp is not a partition column, filtering on it should still return results if the data matches the filter condition.
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. Permission issues cause access denied errors, not zero results.
- ✗
Athena cannot query nested JSON objects.
Why it's wrong here
Incorrect. Athena can query nested JSON using dot notation or the t.* syntax.
- ✓
The JSON files are not in the correct format for Athena.
Why this is correct
Correct. JSON files may have timestamps in an unsupported format or structural issues preventing proper parsing.
- ✗
The 'timestamp' field is not defined as a partition column in the Glue table.
Why it's wrong here
Incorrect. While partition pruning helps performance, filtering on a non-partition column still scans data and returns matching rows.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This MLS-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 MLS-C01 exam.