In DAX expressions, how are variables defined?

In DAX, variables are defined using the VAR function. This function allows users to create a variable that stores a value or result of an expression, which can then be reused within the scope of the DAX expression where it was defined. Utilizing variables helps improve the readability and efficiency of DAX code by allowing complex expressions to be broken down into simpler parts.

By defining a variable with the VAR function, you can use a name to reference that variable multiple times later in your DAX expression without recomputing the value. This leads to better performance, especially when dealing with calculations that involve large datasets or complex operations.

Other functions mentioned, such as the LET function, do not exist in DAX, while SUMMARIZE and FILTER are specific functions used for aggregating and filtering data but do not define variables. Understanding how to use the VAR function is essential for effective DAX coding, especially in developing measures and calculated columns in tools like Power BI.