The answer is a partition column data type mismatch, which causes Athena to perform a full scan instead of pruning partitions. When the table definition declares the day partition as a string but the actual S3 folder names use a different format—like numeric values without leading zeros—Athena cannot match the WHERE clause filter to the partitions, so it reads all data. This excessive data scan type mismatch is a classic trap on the AWS Certified Data Engineer Associate DEA-C01 exam, testing your understanding of how partition pruning depends on exact type alignment between the table schema and folder structure. A common mistake is assuming any filter on a partition column automatically triggers pruning, but Athena requires the data type in the DDL to match the folder naming convention exactly. Remember the mnemonic: "Type must tie to prune the sky"—if the partition column type doesn't tie to the folder format, Athena scans the entire sky of data.
DEA-C01 Data Operations and Support Practice Question
This DEA-C01 practice question tests your understanding of data operations and support. 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 notices that an Amazon Athena query on a partitioned table in S3 scans more data than expected. The table is partitioned by year, month, day. The query includes a WHERE clause on a non-partition column but also filters on day='2023-01-01'. What is the most likely cause of the excessive data scan?
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 partition column data type in the table definition does not match the actual partition folder names
Option D is correct because mismatched data types cause partition pruning to fail. Option A is wrong because partition pruning works with proper types. Option B is wrong because it would not affect scan size. Option C is wrong because sorting is irrelevant.
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 data is stored in JSON format instead of Parquet
Why it's wrong here
Format affects scan but not partition pruning.
✗
The table is not partitioned by the column used in the WHERE clause
Why it's wrong here
It is partitioned by day, but the issue is type mismatch.
✓
The partition column data type in the table definition does not match the actual partition folder names
Why this is correct
If the partition column is defined as string but folders are dates, pruning fails and full scan occurs.
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 data is not sorted within partitions
Why it's wrong here
Sorting does not affect partition pruning.
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 DEA-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 Operations and Support — This question tests Data Operations and Support — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The partition column data type in the table definition does not match the actual partition folder names — Option D is correct because mismatched data types cause partition pruning to fail. Option A is wrong because partition pruning works with proper types. Option B is wrong because it would not affect scan size. Option C is wrong because sorting is irrelevant.
What should I do if I get this DEA-C01 question wrong?
Identify which DEA-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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