This MLS-C01 practice question tests your understanding of exploratory data analysis. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: cOUNT(*). 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.
The exhibit shows an Athena query result from a table. What is the output of the query?
3, 3, 4
Why wrong: COUNT(col2) is 2, not 3; COUNT(*) is 4, not 3.
2, 3, 3
Why wrong: COUNT(*) is 4, not 3; distinct col1 is 4, not 3.
2, 4, 4
Correct counts: col2 non-null=2, rows=4, distinct col1=4.
2, 4, 3
Why wrong: COUNT(DISTINCT col1) is 4, not 3.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
2, 4, 4
Option C is correct. The query returns COUNT(col2)=2 (only rows 1 and 3 have non-null col2), COUNT(*)=4 (total rows), COUNT(DISTINCT col1)=4 (distinct values A, B, C, D). Option A is wrong because COUNT(col2) is 2, not 3. Option B is wrong because COUNT(*) is 4, not 3. Option D is wrong because COUNT(DISTINCT col1) is 4, not 3.
Key principle: COUNT(*)
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
3, 3, 4
Why it's wrong here
COUNT(col2) is 2, not 3; COUNT(*) is 4, not 3.
2, 3, 3
Why it's wrong here
COUNT(*) is 4, not 3; distinct col1 is 4, not 3.
2, 4, 4
Why this is correct
Correct counts: col2 non-null=2, rows=4, distinct col1=4.
Related concept
COUNT(*)
2, 4, 3
Why it's wrong here
COUNT(DISTINCT col1) is 4, not 3.
Common exam traps
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
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
Key takeaway
COUNT(*)
Real-world example
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. COUNT(*) 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
Review cOUNT(*), then practise related MLS-C01 questions on the same topic to reinforce the concept.
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FAQ
Exploratory Data Analysis — This question tests Exploratory Data Analysis — COUNT(*).
The correct answer is: 2, 4, 4 — Option C is correct. The query returns COUNT(col2)=2 (only rows 1 and 3 have non-null col2), COUNT(*)=4 (total rows), COUNT(DISTINCT col1)=4 (distinct values A, B, C, D). Option A is wrong because COUNT(col2) is 2, not 3. Option B is wrong because COUNT(*) is 4, not 3. Option D is wrong because COUNT(DISTINCT col1) is 4, not 3.
Review cOUNT(*), then practise related MLS-C01 questions on the same topic to reinforce the concept.
COUNT(*)
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Last reviewed: Jun 20, 2026
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