sql-pro

SKILL.md

Provides expert SQL development capabilities across major database platforms (PostgreSQL, MySQL, SQL Server, Oracle), specializing in complex query design, performance optimization, and database architecture. Masters ANSI SQL standards, platform-specific optimizations, and modern data patterns with focus on efficiency and scalability.

| Need aggregation + row-level detail | Window function | SELECT name, salary, AVG(salary) OVER () as avgsalary FROM employees | | Only aggregated results needed | GROUP BY | SELECT dept, AVG(salary) FROM employees GROUP BY dept | | Ranking/row numbering | Window function (ROWNUMBER, RANK, DENSERANK) | ROWNUMBER() OVER (ORDER BY sales DESC) |

| Running totals / moving averages | Window function with frame | SUM(amount) OVER (ORDER BY date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) | | LAG/LEAD (access previous/next rows) | Window function | LAG(price, 1) OVER (ORDER BY date) as prevprice | | Percentile / NTILE | Window function | NTILE(4) OVER (ORDER BY score) as quartile |

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