The answer is to check the data types of the columns in the WHERE clause, manually verify the S3 files exist, and run MSCK REPAIR TABLE. When an Athena query returns zero rows for a partition that should contain data, the most common technical cause is a data type mismatch—for example, querying a date partition column as a string when the partition is stored as a timestamp, which silently filters out all rows. Another frequent issue is that the partition metadata in the Glue Catalog is missing or outdated, so MSCK REPAIR TABLE is needed to register new partitions added directly to S3. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of how Athena’s schema-on-read engine interacts with partitioned data, often appearing as a multi-select question where the trap is assuming the query automatically updates partitions or that converting to Parquet is a troubleshooting step. Remember the mnemonic “Check, Confirm, Repair” to recall the three steps: check data types, confirm files exist, and repair the table metadata.
MLS-C01 Exploratory Data Analysis Practice Question
This MLS-C01 practice question tests your understanding of exploratory data analysis. 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 performing EDA on a dataset stored in Amazon S3 using Amazon Athena. The dataset is partitioned by date, and each partition contains CSV files. The data scientist notices that some queries return zero rows for partitions that should have data. Which THREE steps should the data scientist take to troubleshoot? (Choose 3.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Verify that the CSV files exist in the S3 bucket for the specific partition.
Option A is correct because manually checking files confirms data presence. Option B is correct because MSCK REPAIR TABLE adds partitions not yet registered. Option C is correct because incorrect data types can cause filters to exclude rows. Option D is wrong because the query does not automatically update partitions. Option E is wrong because converting to Parquet is not a troubleshooting step.
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.
✓
Verify that the CSV files exist in the S3 bucket for the specific partition.
Why this is correct
Files may have been moved or deleted.
Related concept
Read the scenario before looking for a memorised answer.
✓
Run MSCK REPAIR TABLE to add new partitions to the Glue Data Catalog.
Why this is correct
Partitions may not have been discovered by the crawler.
Related concept
Read the scenario before looking for a memorised answer.
✗
Convert the CSV files to Parquet format.
Why it's wrong here
Format conversion is not a troubleshooting step for missing data.
✓
Check the data types of the columns used in the query's WHERE clause.
Why this is correct
Type mismatches can cause the filter to exclude all rows.
Related concept
Read the scenario before looking for a memorised answer.
✗
Re-run the query with a LIMIT clause to force partition discovery.
Why it's wrong here
LIMIT does not trigger partition discovery.
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.
Exploratory Data Analysis — This question tests Exploratory Data Analysis — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Verify that the CSV files exist in the S3 bucket for the specific partition. — Option A is correct because manually checking files confirms data presence. Option B is correct because MSCK REPAIR TABLE adds partitions not yet registered. Option C is correct because incorrect data types can cause filters to exclude rows. Option D is wrong because the query does not automatically update partitions. Option E is wrong because converting to Parquet is not a troubleshooting step.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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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.
Question Discussion
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