PowerPivot - DAX (first time)

One 、 Introduce

        1、 summary

         Data analysis expressions (DAX) Is in Analysis Services、Power BI as well as Excel Medium Power Pivot Formula expression language used . DAX Formulas include functions 、 Operators and values , It is used to perform advanced calculations and queries on the data in related tables and columns in the table data model .

        2、 The formula

        DAX Formulas are important for creating calculations in calculated columns and measures and protecting data with row level security . To create formulas for calculating columns and measures , Please use the formula bar at the top of the model designer window or DAX Editor .

        3、 Basic knowledge of formulas          

         Whether the formula created is simple or complex , You can generate formulas according to the following steps ：

                ① Each formula must be marked with an equal sign (=) start .

                ② You can type or select a function name , You can also type an expression .

                ③ Start typing the first few letters of the desired function or name , The autocomplete function will show the available functions 、 List of tables and columns . Press Tab Key to add items from the autocomplete list to the formula .

                 You can also click Fx The button displays a list of available functions . To select a function from the drop-down list , Please use the arrow keys to highlight the item , And then click “ determine ” Add this function to the formula .

                ④ By selecting parameters from the drop-down list of possible tables and columns , Or by typing a value , Give the function parameters .

                ⑤ Check for grammatical errors ： Make sure all parentheses are paired , And the column is referenced correctly 、 Table and value .

                ⑥ Press Enter Key accepts the formula .

          example ：

Days in Current Quarter = COUNTROWS( DATESBETWEEN( 'Date'[Date], STARTOFQUARTER( LASTDATE('Date'[Date])), ENDOFQUARTER('Date'[Date])))

         This measure is used to create a comparison ratio between an incomplete period and the previous period . The formula must consider the proportion of the elapsed time period , And compare it with the same proportion in the previous period .

 

Two 、DAX Operator

        1、 Definition

         Data analysis expressions (DAX) Language uses operators to create comparison values 、 Expressions that perform arithmetic calculations or process strings .

        2、 Operator type

         There are four different types of operators ： Arithmetic operator 、 Comparison operator 、 Text concatenation operator and logical operator .

        3、 Arithmetic operator

         To perform basic mathematical operations （ Such as addition 、 Subtraction or multiplication ）、 Combine numbers and generate numerical results , Please use the following arithmetic operators .

        

        4、 Comparison operator  

          You can use the following operators to compare two values . When comparing two values using these operators , The result is a logical value （TRUE or FALSE）.

        

        5、 Text concatenation operator

         Use and (&) Join or concatenate two or more text strings to produce a single text segment .

         

        6、 Logical operators  

         Use logical operators （&&） and (||) Combine expressions to produce a single result .