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DA0-002 Data Acquisition and Preparation Practice Question

During data profiling, an analyst wants to identify the number of distinct values in a column. Which SQL function should be used?

⚠ Common exam trap

DA0-002 often tests the difference between COUNT(*), COUNT(column), and COUNT(DISTINCT column) — candidates must remember that only COUNT(DISTINCT) deduplicates values.

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

✓

COUNT(DISTINCT column)

COUNT(DISTINCT column) returns the number of unique non-null values in a column, which is exactly what data profiling requires to measure cardinality. It is the standard SQL aggregate for distinct value counts.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✗

    DISTINCT(column)

    Why it's wrong here

    DISTINCT is a SELECT clause keyword that returns the unique rows themselves, not a count of them, so it cannot yield the number of distinct values. It is tempting because it does eliminate duplicates, and it would be correct if the analyst needed the actual list of unique values rather than their quantity.

  • ✓

    COUNT(DISTINCT column)

    Why this is correct

    COUNT(DISTINCT column) returns the cardinality of a column by eliminating duplicate values before counting, directly satisfying the requirement to identify the number of distinct values during data profiling. Unlike COUNT(*), which counts every row including repeats, this aggregate yields the unique-value total the analyst needs.

  • ✗

    COUNT(*)

    Why it's wrong here

    COUNT(*) returns the total number of rows in the table or group, including duplicates and NULLs, so it never measures distinct values. It is tempting because it is the standard way to count rows, and it would be correct if the analyst simply needed the overall record count during profiling.

  • ✗

    COUNT(column)

    Why it's wrong here

    COUNT(column) tallies non-NULL rows in that column, counting every repeated value separately, so it returns the row population rather than the number of distinct values. It is tempting because COUNT is the right aggregate family, and COUNT(column) would be correct if the analyst wanted to know how many rows contain a non-NULL entry.

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Written and reviewed by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

Last reviewed September 2026 · checked against the official CompTIA exam blueprint

This DA0-002 practice question is part of Courseiva's free CompTIA 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 DA0-002 exam.