Interview Questions - DAX in Power BI - Part 1

Here are some possible interview questions and answers about DAX in Power BI based on my experience and understanding.


You have practice and study a lot before any interview, but still, you are thinking about what could be the questions on DAX. 

For most of the Power BI jobs, if you observe, they mention specifically DAX as one of the skill sets. That means you need to concentrate on this area more in comparison with others.

In this blog, I am going to start with capture some possible questions and answers on DAX in Power BI. I cannot say that these are obvious questions but from an interviewer perspective, I will look for some candidates who have this knowledge. 

Let’s start with some basic questions. 


Question 1: What is DAX?

Answer: The acronym of DAX is Data Analysis Expressions. It is known as a functional language. It means, calculations mostly use functions to generate the results. It is also called an expression language.

Question 2: Why are you using DAX? or What is the purpose of DAX? 

DAX is designed for enhancing data modelling, reporting and analytics capability. DAX helps to get more insights into your data that you wouldn’t otherwise be able to get. For example, enabling time intelligence capability.

Question 3: Are there specific data types for DAX?

Yes, some data types are supported by DAX. Those are 7 types, whole number, decimal number, boolean, text, date, currency, N/A (Blank).

Question 4: Is it possible to define data type in DAX? Is there any benefit to that?

Yes, it is possible to define the data type for each column based on the requirement.

The selection of the best data type helps to reduce the size of a data model and improve the performance when to refresh data and use of any report.

Question 5: How many types of operators are we using in DAX?

There are 4 categories of DAX operators, comparison operators, arithmetic operators, text operators, and logical operators.

Question 6: How many function categories are there in DAX?

As per Microsoft documentation, there are 14 types of function categories in DAX. Out of them, we are using mostly 9 function categories in Power BI. 

  1. Date and Time
  2. Time Intelligence
  3. Information
  4. Logical
  5. Mathematical
  6. Statistical
  7. Text
  8. Parent/Child
  9. Other

Question 7: Are you following any data model concept when you are writing DAX functions? If yes, do you know how many components are there?

Yes, the DAX function supports a data model concept. Just like one data model, it has data, tables, columns, relationships, measures, hierarchies. As we know, a data model consists of data, calculations and formatting rules and it combines to create an object. This object helps to explore and understand the dataset.

Question 8: Do you know about M? Is there any difference between M and DAX? 

Yes, in Power Query, we are writing the script which is known as M language or Power Query Formula language. 

There is some difference between M and DAX. 

M language is normally used for data transformation, we can typically say, it is for ETL. 

Whereas DAX is used for data analysing purposes, which means using different DAX functions we can analyse data more effectively.

Question 9: How do you know in which scenario we need to use M or DAX?

Both languages are valued based on their usages.

 For example, if we want to create one flag column based on some existing columns values, then it is preferable to create in Power Query Editor using M. Here we are transforming the data.

 Let’s consider another example where we want to provide year on year or month on month analysis. In this case, DAX is ideal because it has time intelligence functions for implement this. 

So after analysing the requirements, we can decide the best way to implement them. We need to learn both languages. 

Question 10: What is DAX Variable?

In DAX calculation, we can use variables to make the calculations easier to understand.

When you are writing any complex or nested expression using DAX functions, variables can help to break these complex calculations into smaller, more useful sections.

Question 11: Why do we need the DAX variable?

There are main 4 reasons to use DAX variables.

  1. Reduce Complexity
  2. Easy to Debug
  3. Improve Readability
  4. Improve Performance 

Question 12: Give one example of a variable usage scenario?

You can visit my blog about DAX Variable for different examples. It is better to practice before going for an interview.

https://arpitatechcorner.com/2021/04/22/use-of-dax-variable-in-power-bi/

Conclusion

In this blog, we get some idea about 12 interview questions on DAX. We will know more DAX interview questions in the next blog.

If you have any questions related to this project, please feel free to post your comments.

Please like, comment and subscribe to my YouTube channel which you have already seen. 🙂 Keep Learning.

3 comments

  1. Thank you so much for this. Regards Laxman

    On Sat, Sep 4, 2021, 2:20 AM Arpita’s Tech Corner wrote:

    > Arpita Ghosh posted: ” Here are some possible interview questions and > answers about DAX in Power BI based on my experience and understanding. You > have practice and study a lot before any interview, but still, you are > thinking about what could be the questions on DAX.&nb” >

    Like

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