DA0-002 Data Acquisition and Preparation Practice Question
A data analyst is extracting data from a relational database using SQL. Which clause is essential for limiting the rows retrieved to only those needed?
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
✓
WHERE
WHERE. The WHERE clause is used to filter rows from a table based on specified conditions, limiting the result set to only the rows that meet those conditions. Option A (GROUP BY) is incorrect because it groups rows with same values into summary rows, not for filtering. Option B (ORDER BY) is incorrect because it sorts the result set, not filters. Option D (HAVING) is incorrect because it filters groups after aggregation, not individual rows. Therefore, WHERE is essential for limiting rows retrieved.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
GROUP BY
Why it's wrong here
GROUP BY collapses rows into aggregated groups rather than filtering which source rows qualify. It is tempting because it does reduce the visible row count, and would be correct for producing per-category summaries, but restricting rows to those needed is the WHERE clause's role.
- ✗
ORDER BY
Why it's wrong here
ORDER BY sorts the result set but returns every qualifying row, so it cannot reduce the count retrieved. It is tempting because it shapes output and pairs with TOP for pagination, and would be correct when presenting sorted data, but limiting rows requires the WHERE clause.
- ✓
WHERE
Why this is correct
The WHERE clause applies row-level predicates, filtering records so only those matching specified conditions are returned. It satisfies the requirement to limit retrieved rows, reducing data transfer and processing compared with retrieving the full table.
- ✗
HAVING
Why it's wrong here
HAVING filters grouped rows after aggregation, so it cannot restrict individual source rows before grouping. It is tempting because it does limit result rows, and would be correct for filtering aggregate values such as totals per category, but row-level restriction belongs in the WHERE clause.
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