DA0-002 Data Acquisition and Preparation Practice Question
In a table 'employee_hierarchy' with columns 'employee_id', 'manager_id', and 'employee_name', an analyst needs to generate a list of all employees under a specific manager, including multiple levels of subordinates. Which SQL construct is most appropriate for querying this hierarchical data efficiently?
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
✓
Recursive CTE
Recursive CTEs are designed to handle hierarchical data by repeatedly joining a CTE to itself until all levels are included.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Recursive CTE
Why this is correct
A recursive CTE satisfies the multi-level requirement by self-referencing: the anchor member selects direct subordinates where manager_id matches the given manager, then the recursive member joins employee_hierarchy back to the CTE on manager_id = employee_id, iterating until no rows return. This traverses the full hierarchy in one statement, unlike fixed self-joins.
- ✗
Window function with PARTITION BY
Why it's wrong here
PARTITION BY groups rows for ranking or aggregation within the current result set; it does not traverse parent-child links, so it cannot discover subordinates at arbitrary depths. It is tempting because window functions elegantly handle running totals and per-group rankings, which is what they are actually designed for.
- ✗
Subquery in WHERE clause
Why it's wrong here
A correlated subquery in WHERE evaluates a single scalar comparison and cannot return the full recursive set of descendants across multiple levels. It is tempting because subqueries handle simple membership tests neatly, and they would be correct for filtering employees whose manager_id matches one specific identifier.
- ✗
Self-JOIN with WHERE clause
Why it's wrong here
A self-JOIN returns only one level of subordinates per join, so recursion depth must be hard-coded and unknown hierarchy depths are missed. It is tempting because self-JOINs are the classic pre-CTE technique for parent-child rows, and they remain correct for fixed-depth relationships such as employee-to-immediate-manager lookups.
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