Power BI DAX

What is DAX?

DAX is a collection of functions, operators, and constants that can be used in a formula, or expression, to calculate and return one or more values. Stated more simply, DAX helps you create new information from data already in your model.

Syntax

Before you create your own formulas, let’s take a look at DAX formula syntax. Syntax includes the various elements that make up a formula, or more simply, how the formula is written. For example, here's a simple DAX formula for a measure:

This formula includes the following syntax elements:

A. The measure name, Total Sales.

B. The equals sign operator (=), which indicates the beginning of the formula. When calculated, it will return a result.

C. The DAX function SUM, which adds up all of the numbers in the Sales[SalesAmount] column. You’ll learn more about functions later.

D. Parenthesis (), which surround an expression that contains one or more arguments. All functions require at least one argument. An argument passes a value to a function.

E. The referenced table, Sales.

F. The referenced column, [SalesAmount], in the Sales table. With this argument, the SUM function knows on which column to aggregate a SUM.

This name is known as a fully qualified column name in that it includes the column name preceded by the table name.  Columns referenced in the same table don't require the table name be included in the formula, which can make long formulas that reference many columns shorter and easier to read. However, it's a good practice to include the table name in your measure formulas, even when in the same table.

When trying to understand a DAX formula, it's often helpful to break down each of the elements into a language you think and speak every day. For example, you can read this formula as:

For the measure named Total Sales, calculate (=) the SUM of values in the [SalesAmount ] column in the Sales table.