SQL Window Functions: A Practical Guide
Window functions are one of the most powerful and underused features in SQL. Unlike GROUP BY, they let you perform calculations across a set of rows related to the current row — without collapsing the result set. The Core Syntax function_name() OVER ( PARTITION BY column1 ORDER BY column2 ROWS/RANGE BETWEEN ... AND ... ) Clause Purpose Required? PARTITION BY Divides rows into groups (like GROUP BY, but rows are kept) No ORDER BY Defines the order within each partition Depends on function Frame (ROWS BETWEEN) Defines which rows to include relative to the current row No 1. Ranking Functions ROW_NUMBER() Assigns a unique sequential integer to each row within a partition. No ties. ...