DA0-002 Data Acquisition and Preparation Practice Question
A data analyst needs to count the number of distinct product categories in a table named 'products'. Which SQL function should be used in the SELECT clause?
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 category)
COUNT(DISTINCT column) counts unique non-null values in a column.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
COUNT(category)
Why it's wrong here
This counts all non-null category values, including duplicates.
- ✗
DISTINCT COUNT(category)
Why it's wrong here
Invalid SQL syntax.
- ✓
COUNT(DISTINCT category)
Why this is correct
This counts only unique non-null categories.
- ✗
COUNT(*) WHERE category IS NOT NULL
Why it's wrong here
This would count all rows with a non-null category, not distinct values.
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