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Friday, June 23, 2017

How to handle NULL in SSAS Tabular by using DAX

As new in DAX area, I found a few useful DAX function that can ease your BI life while you are working with SSAS Tabular model. To handle null values and undefined values were challenging at the begining, however: found two useful function called ISBLANK and IF that you can use to handle those challenges.

Let's discuss with example: a table named Dim_Account which has data like below (In real life you may not have this type of data, however, you get problem when your data is corrupted)

Fig 1: Account data (corrupted)


Now I would like to count number of rows from the above dataset where AccNo is not NULL,and AccTypeName='Savings'

So the DAX look like: COUNTAX(FILTER(Dim_Account;[AccTypeName]="Savings");[AccNo]))

Here, COUNTAX calculate only non empty rows so I got number of row return =1; however; I would like see how many rows also have NULL, and would like to replace the NULL value with 0.

How do you do? There is a function in DAX which is ISNULL. So lets handle the NULL value in DAX:

IF(ISBLANK(COUNTAX(FILTER(Dim_Account;[AccTypeName]="Savings");[AccNo]));0;COUNTAX(FILTER(Dim_Account;[AccTypeName]="Savings");[AccNo])))

If you are coming from SQL background then surely you say NULL and BLANK are not same, they are completely different.. However; here is the reference from Microsoft DAX:

"A blank is a data type in DAX that represents and replaces SQL nulls. You can create a blank by using the BLANK function, and test for blanks by using the logical function, ISBLANK."


However, Lets look into the details regarding function IF(ISBLANK(A);0;A), it means if A is NULL then return 0 and all other cases get the value of A.

At the same way, If we explain DAX for accountype NULL handles:

Fig 2. DAX Null handles

From the above fig 2: first part of the DAX query is traverse through each row of the table and find if any NULL value and then replace that with 0 and the last part is execute if first part is FALSE, it means get all the value than NULL.


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