Multiple window functions in one query

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Accepted Answer

Window functions are independent: each one defines its own partition, order, and frame via its own OVER clause. A single SELECT can mix ROW_NUMBER() OVER (PARTITION BY dept ORDER BY salary), LAG(salary) OVER (ORDER BY hire_date), and SUM(sales) OVER (PARTITION BY region ORDER BY month ROWS BETWEEN 2 PRECEDING AND CURRENT ROW) simultaneously. The WINDOW keyword (supported in PostgreSQL and others) lets you name a window spec and reuse it to avoid repetition when multiple functions share the same OVER clause.