Window Function
Introduction When using GROUP BY to aggregate duplicate data rows, relevant individual data rows are lost. Window Function is used to overcome this limitation. It helps perform aggregation calculations on a set of related rows while preserving the original data rows without collapsing them. Window Function executes after WHERE, GROUP BY and HAVING clauses, but before DISTINCT and ORDER BY in the main statement. Therefore, you cannot place a Window Function directly inside the WHERE clause. If you want to filter data based on the result of a Window Function , you must use a temporary table such as a CTE or Subquery . How to Use To construct a Window Function , combine a Function and a Clause as follows: SELECT FUNCTION () OVER ( PARTITION BY col1 ORDER BY col2 ROWS / RANGE BETWEEN < START > AND < END > ) AS col_name FROM table_name; Function : The function placed before the OVER keyword, such as SUM(), AVG(), ROW_NUMBER(...