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With DAX, there are many functions available to shape, form, or otherwise analyze your data. These functions can be grouped into a handful of categories:
- Aggregation functions
- Counting functions
- Logical functions
- Information functions
- Text functions
- Date functions
Similar to Excel, when you start typing your formula into the Power BI Desktop Formula Bar, a list of available functions appears to help you determine which available function you want to select. And by using the up and down arrow keys on your keyboard, you can highlight any of the available functions, and a brief description is displayed.
Power BI displays the functions that match the letters you've typed so far, so if you type S only functions that begin with S appear in the list. If you type Su, only functions that contain the letter sequence Su in their name appear in the list (they don't have to start with Su, they just have to contain that letter sequence).
It's easy to experiment with DAX in this way, and to find each of the various DAX functions that are available in Power BI. All you have to do is start typing, and Power BI helps you along.
Now that we know how to get that DAX formula started, let's take a look at each of these function categories in turn.
Aggregation functions
DAX has a number of aggregation functions, including the following commonly used functions:
- SUM
- AVERAGE
- MIN
- MAX
- SUMX (and other X functions)
These functions work only on numeric columns, and generally can aggregate only one column at a time.
However, special aggregation functions that end in X, such as SUMX, can work on multiple columns. These functions iterate through the table, and evaluate the expression for each row.
Counting functions
Often-used counting functions in DAX include the following:
- COUNT
- COUNTA
- COUNTBLANK
- COUNTROWS
- DISTINCTCOUNT
These functions count different elements, such as distinct values, non-empty values, and table rows.
Logical functions
The collection of logical functions in DAX include:
- AND
- OR
- NOT
- IF
- IFERROR
These special functions can also be expressed with operators. For example, AND can be typed as (replaced with) && in your DAX formula.
You can use operators (such as &&) when you need more than two conditions in your formula, but otherwise, it's best practice use the function name itself (such as AND) for readability of your DAX code.
Information functions
Information functions in DAX include:
- ISBLANK
- ISNUMBER
- ISTEXT
- ISNONTEXT
- ISERROR
While these functions can be situationally useful, there is value in knowing the data type of your columns ahead of time, rather than depending on these functions to provide the data type.
DAX uses the MAX and MIN functions to both aggregate values, and to compare values.
Text functions
The text functions in DAX include the following:
- CONCATENTATE
- REPLACE
- SEARCH
- UPPER
- FIXED
These text work very similarly to the Excel functions that have the same name, so if you're familiar with how Excel handles text functions, you're already a step ahead. If not, you can always experiment with these functions in Power BI, and learn more about how they behave.
Date functions
DAX includes the following Date functions:
- DATE
- HOUR
- NOW
- EOMONTH
- WEEKDAY
While these functions are useful to calculate and extract information from date values, they do not apply to time intelligence, which uses a date table.
Video content courtesy of Alberto Ferrari, SQLBI