The December 2022 release of Power BI Desktop includes three new DAX functions: OFFSET, INDEX, and WINDOW. They are collectively called window functions because they are closely related to SQL window functions, a powerful feature of the SQL language that allows users to perform calculations on a set of rows that are related to the current row. Because these functions are often used for data analysis, they are sometimes called analytical functions. In contrast, DAX, a language invented specifically for data analysis, had been missing similar functionalities. As a result, users found it hard to write cross-row calculations, such as calculating the difference of the values of a column between two rows or the moving average of the values of a column over a set of rows.
Read on to learn more about how these functions work and how they differ from their SQL Server counterparts.