Top DAX frequently asked interview questions

In this post we will look at DAX Interview questions. Examples are provided with explanation.

1. What are some of the most commonly used DAX Functions?
2. Are DAX Functions case sensitive?
3. What is the concept of Row Context?
4. Which DAX Functions do not return a table?
5. What are DAX Aggregation Functions?
6. How do DAX Functions differ from Excel Functions?
7. When should M or DAX be used?
8. What is DAX?
9. What is the purpose of a DAX Function?
10. What is Query Context?

What are some of the most commonly used DAX Functions?

The most commonly used DAX functions are SUM, AVERAGE, MIN, MAX, COUNT, COUNTA, DISTINCTCOUNT, FILTER, and CALCULATE. These functions are used to perform calculations on data in a Power BI data model. For example, the SUM function can be used to calculate the total of a given column in a table. The syntax for the SUM function is:

SUM(<column>)

The AVERAGE function can be used to calculate the average of a given column in a table. The syntax for the AVERAGE function is:

AVERAGE(<column>)

The MIN and MAX functions can be used to calculate the minimum and maximum values of a given column in a table. The syntax for the MIN and MAX functions is:

MIN(<column>)
MAX(<column>)

The COUNT and COUNTA functions can be used to count the number of rows in a table. The syntax for the COUNT and COUNTA functions is:

COUNT(<column>)
COUNTA(<column>)

The DISTINCTCOUNT function can be used to count the number of distinct values in a column. The syntax for the DISTINCTCOUNT function is:

DISTINCTCOUNT(<column>)

The FILTER function can be used to filter a table based

Are DAX Functions case sensitive?

Yes, DAX functions are case sensitive. This means that when using DAX functions, the capitalization of the function name and any parameters must match exactly. For example, if you are using the SUM function, the capitalization must be "SUM" and not "sum" or "Sum". The same applies to any parameters that are passed to the function. For example, if you are using the SUM function to calculate the total of a column in a table, the column name must be specified exactly as it appears in the table. For example, if the column name is "TotalSales", the parameter must be specified as "TotalSales" and not "totalsales" or "Totalsales". Using the wrong capitalization when using DAX functions can lead to unexpected results or errors. Therefore, it is important to make sure that the capitalization of the function name and any parameters is correct when using DAX functions.

What is the concept of Row Context?

Row context is a concept in DAX that refers to the current row in a table or data set. When a DAX expression is evaluated, the row context is used to determine which row in the table or data set should be used in the calculation. For example, if you are using the SUM function to calculate the total of a column in a table, the row context will determine which row in the table should be used in the calculation. The syntax for the SUM function is:

SUM(<column>)

In this example, the <column> parameter is used to specify the column that should be used in the calculation. The row context will determine which row in the table should be used in the calculation. The row context can also be used in more complex calculations, such as when using the FILTER function to filter a table based on a condition. The syntax for the FILTER function is:

FILTER(<table>, <condition>)

In this example, the <condition> parameter is used to specify the condition that should be used to filter the table. The row context will determine which rows in the table should be included in the calculation.

Which DAX Functions do not return a table?

There are several DAX functions that do not return a table. These functions are typically used to perform calculations on data in a Power BI data model. The most common DAX functions that do not return a table are SUM, AVERAGE, MIN, MAX, COUNT, COUNTA, DISTINCTCOUNT, and CALCULATE. For example, the SUM function can be used to calculate the total of a given column in a table. The syntax for the SUM function is:

SUM(<column>)

The AVERAGE function can be used to calculate the average of a given column in a table. The syntax for the AVERAGE function is:

AVERAGE(<column>)

The MIN and MAX functions can be used to calculate the minimum and maximum values of a given column in a table. The syntax for the MIN and MAX functions is:

MIN(<column>)
MAX(<column>)

The COUNT and COUNTA functions can be used to count the number of rows in a table. The syntax for the COUNT and COUNTA functions is:

COUNT(<column>)
COUNTA(<column>)

What are DAX Aggregation Functions?

DAX Aggregation Functions are a set of functions that are used to perform calculations on data in a Power BI data model. These functions are used to aggregate data from multiple rows into a single value. The most common DAX Aggregation Functions are SUM, AVERAGE, MIN, MAX, COUNT, COUNTA, and DISTINCTCOUNT. For example, the SUM function can be used to calculate the total of a given column in a table. The syntax for the SUM function is:

SUM(<column>)

The AVERAGE function can be used to calculate the average of a given column in a table. The syntax for the AVERAGE function is:

AVERAGE(<column>)

The MIN and MAX functions can be used to calculate the minimum and maximum values of a given column in a table. The syntax for the MIN and MAX functions is:

MIN(<column>)
MAX(<column>)

The COUNT and COUNTA functions can be used to count the number of rows in a table. The syntax for the COUNT and COUNTA functions is:

COUNT(<column>)
COUNTA(<column>)

How do DAX Functions differ from Excel Functions?

DAX functions are different from Excel functions in several ways.
First - DAX functions are designed to work with data in a Power BI data model, while Excel functions are designed to work with data in a spreadsheet. This means that DAX functions are optimized for working with large amounts of data, while Excel functions are optimized for working with small amounts of data.
Second - DAX functions are designed to be used in calculated columns and measures, while Excel functions are designed to be used in worksheet cells. This means that DAX functions can be used to perform calculations on data in a Power BI data model, while Excel functions can be used to perform calculations on data in a spreadsheet.
Third - DAX functions are designed to work with tables and columns, while Excel functions are designed to work with individual cells. This means that DAX functions can be used to perform calculations on multiple rows of data at once, while Excel functions can only be used to perform calculations on a single cell at a time.
Finally, DAX functions are designed to be used in calculated columns and measures, while Excel functions are designed to be used in worksheet cells. This means that DAX functions can be used to create calculated columns and measures that can be used to analyze data in a Power BI data model, while Excel functions can only be used to perform calculations on data in a spreadsheet.

When should M or DAX be used?

M and DAX are two different languages that can be used to create calculations in Power BI. M is a language that is used to create custom functions and calculations, while DAX is a language that is used to create calculated columns and measures.
M should be used when you need to create custom functions or calculations that are not available in DAX. For example, if you need to create a custom function to calculate the total sales for a given period, you would use M.
DAX should be used when you need to create calculated columns or measures. For example, if you need to create a calculated column to calculate the total sales for a given period, you would use DAX.
In general, M should be used when you need to create custom functions or calculations, and DAX should be used when you need to create calculated columns or measures. Both M and DAX can be used to create powerful calculations in Power BI, but they should be used for different purposes.

What is DAX?

DAX stands for Data Analysis Expressions and is a language used to create calculations in Power BI. DAX is used to create calculated columns and measures, which are used to analyze data in a Power BI data model.
DAX is a powerful language that allows users to create complex calculations on data in a Power BI data model. It is designed to be used in calculated columns and measures, and is optimized for working with large amounts of data.
DAX includes a wide range of functions that can be used to perform calculations on data in a Power BI data model. These functions include SUM, AVERAGE, MIN, MAX, COUNT, COUNTA, DISTINCTCOUNT, FILTER, and CALCULATE.
DAX is a powerful language that can be used to create powerful calculations in Power BI. It is designed to be used in calculated columns and measures, and is optimized for working with large amounts of data. With DAX, users can create complex calculations on data in a Power BI data model.

What is the purpose of a DAX Function?

The purpose of a DAX function is to perform calculations on data in a Power BI data model. DAX functions are used to aggregate data from multiple rows into a single value, calculate the total of a given column in a table, calculate the average of a given column in a table, calculate the minimum and maximum values of a given column in a table, count the number of rows in a table, count the number of distinct values in a column, and filter a table based on a condition. DAX functions are designed to be used in calculated columns and measures, and are optimized for working with large amounts of data. With DAX, users can create powerful calculations on data in a Power BI data model.

How does Dax compare to SQL?

SQL is designed to be used to query data from a database. It includes a wide range of commands that can be used to retrieve data from a database. In general, DAX should be used when you need to create calculated columns or measures, and SQL should be used when you need to query data from a database. Both DAX and SQL can be used to create powerful calculations in Power BI, but they should be used for different purposes.

What is Query Context

Query context is a concept in DAX that refers to the current query in a Power BI data model. When a DAX expression is evaluated, the query context is used to determine which query in the data model should be used in the calculation. For example, if you are using the FILTER function to filter a table based on a condition, the query context will determine which query in the data model should be used in the calculation. The syntax for the FILTER function is:

FILTER(<table>, <condition>)

In this example, the <condition> parameter is used to specify the condition that should be used to filter the table. The query context will determine which query in the data model should be used in the calculation. The query context can also be used in more complex calculations, such as when using the CALCULATE function to calculate a measure. The syntax for the CALCULATE function is:

CALCULATE(<expression>, <filter>)

In this example, the <filter> parameter is used to specify the filter that should be used in the calculation. The query context will determine which query in the data model should be used in the calculation.

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