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SQL Window Function

A window function (ROW_NUMBER, RANK, SUM OVER, LAG) computes a value per row over a partition of related rows defined by OVER (PARTITION BY ... ORDER BY ...), without collapsing rows the way GROUP BY does. This lets rankings and running totals be computed in one pass instead of a self-join or per-row subquery.

Questions this Concept answers

Why do window functions so often add a sort to a plan?

jeremy Video

Ranking Rows in SQL with Window Functions Using OVER PARTITION BY ROW_NUMBER RANK and DENSE_RANK

A SQL window function has two required parts: a function that computes a value for each row, and an `OVER (...)` clause that defines the *window* — the set of rows, and their order, that the function…