**CTEs:** WITH cte AS (...) SELECT ... FROM cte. Readability, reuse, recursion. **Conditional join:** AND in ON, or CASE in ON. Multiple LEFT JOINs with different conditions.
WITH ranked AS (
SELECT *, ROW_NUMBER() OVER (PARTITION BY user_id ORDER BY date DESC) rn
FROM events
)
SELECT r.*, u.name
FROM ranked r
LEFT JOIN users u ON r.user_id = u.id AND u.status = 'active'
WHERE r.rn = 1;
The complete answer continues with detailed implementation patterns, architectural trade-offs, and production-grade considerations. It covers performance optimization strategies, common pitfalls to avoid, and real-world examples from companies like Myntra. The answer also includes follow-up discussion points that interviewers commonly explore.
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