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Write optimized SQL queries involving window functions, CTEs, and joins.

SQLmedium0.3 min readPremium

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487

questions in SQL

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in this category

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1,863

across 7 categories

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Key Concepts Tested

join partition sql window

Expert AnswerPremium

65 wordsInterview-ready

Example—running totals: WITH base AS (SELECT customer_id, order_date, amount, SUM(amount) OVER (PARTITION BY customer_id ORDER BY order_date) AS running_total FROM orders), enriched AS (SELECT b.*, c.tier FROM base b JOIN customers c ON b.customer_id = c.id) SELECT * FROM enriched WHERE running_total > 1000. **Why**: CTEs for readability and optimizer; window over correlated subquery; filter early....

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 Apple. The answer also includes follow-up discussion points that interviewers commonly explore.

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