Answer
A window function calculates across related rows without collapsing them into one row per group. • OVER defines the window specification. • PARTITION BY creates independent partitions. • ORDER BY and a frame can define row sequence and the rows used by the calculation.
💡 SQL Example
SELECT name, salary, AVG(salary) OVER (PARTITION BY department_id) AS department_average FROM employees;
Result
Each employee row with its department average
⚡ Quick Revision
Window functions calculate across row sets while preserving individual rows.