Inner join result?
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of SQL & Databases conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
An INNER JOIN returns only the subset of rows where the join predicate (ON condition) matches in both tables simultaneously:
### Visual Venn Diagram Concept:
If Table A has IDs [1, 2, 3] and Table B has IDs [2, 3, 4], the inner join on A.id = B.id returns only rows for IDs [2, 3].
SELECT e.name, d.dept_name
FROM employees e
INNER JOIN departments d ON e.dept_id = d.id;
If an employee has a NULL or non-existent dept_id, that employee will not appear in the result set.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.