SQL Window Functions and Ranking
SQL window functions and ranking are powerful tools for performing calculations across sets of rows that relate to the current row. Let me break this down into digestible concepts with practical examples. What are Window Functions? Window functions perform calculations across a set of table rows related to the current row, but unlike aggregate functions, they don't collapse rows into a single result. They "look through a window" at related rows while preserving the original row structure. Basic Syntax: function_name() OVER ( [PARTITION BY column1, column2, ...] [ORDER BY column1, column2, ...] [ROWS/RANGE specification] ) Key Components PARTITION BY : Divides the result set into partitions (like GROUP BY, but doesn't collapse rows) ORDER BY : Defines the order within each partition Window Frame : Specifies which rows to include in the calculation (ROWS/RANGE) Ranking Functions 1. ROW_NUMBER() Assigns a unique sequential integer to each row within a partiti...