COUNT() OVER

COUNT() OVER is a SQL function in the Window Functions category. Windowed count — counts rows per partition without collapsing rows. The syntax is COUNT(*) OVER (PARTITION BY column). It accepts *. It returns windowed count. A typical example: SELECT name, dept, salary, COUNT(*) OVER (PARTITION BY dept) AS dept_size FROM employees; -- Each row shows its department's total employee count A close relative is ROW_NUMBER(), which assigns a unique sequential integer to each row within its partition (1, 2, 3...). A close relative is RANK(), which similar to ROW_NUMBER but gives the same rank to equal values. Leaves gaps in ranking. A close relative is DENSE_RANK(), which like RANK but without gaps. Equal values get the same rank, and the next number follows sequentially. More about this category: Window/analytical functions — ROW_NUMBER, RANK, DENSE_RANK, LAG, LEAD, NTILE. Related Window Functions entries: ROW_NUMBER(), RANK(), DENSE_RANK(), LAG(), LEAD(), NTILE(), SUM() OVER, AVG() OVER.