Updating data in pivot table
You can nest up to 64 levels of functions in calculated columns.However, nesting can make it difficult to create or troubleshoot formulas.DAX includes some of the functions used in Excel formulas, and additional functions designed to work with relational data and perform dynamic aggregation. To create one, you type an equal sign, followed by a function name or expression, and any required values or arguments.Like Excel, DAX provides a variety of functions that you can use to work with strings, perform calculations using dates and times, or create conditional values.A measure is used in the Values area of a Pivot Table.
Instead of pasting or importing values in the column, you create a DAX formula that defines the column values.
When you define a formula for an explicit measure, nothing happens until you add the measure into a Pivot Table.
When you add the measure, the formula is evaluated for each cell in the Values area of the Pivot Table.
A measure is a formula that is created specifically for use in a Pivot Table (or Pivot Chart) that uses Power Pivot data.
Measures can be based on standard aggregation functions, such as COUNT or SUM, or you can define your own formula by using DAX.