Thursday 21 December 2023

What is the difference between Distinct() and Values() in DAX? Power BI interview questions and answers 074

 What is the difference between Distinct() and Values() in DAX?

Both DISTINCT() and VALUES() functions in DAX are used to handle duplicate values, but they have subtle differences in their output and behavior. Here's a breakdown:


  • Both functions can take either a column name or a table expression as an argument.


  • DISTINCT(): Removes duplicate rows (all columns) based on the specified column(s) or table and returns a new table with only unique rows. Duplicate values within a row are also treated as non-unique.

  • VALUES(): Primarily removes duplicate values from the specified column and returns a one-column table with unique values. However, there are two key additional points:

  • It also includes a special BLANK value in the output if there are missing values in the specified column due to relationship issues.

  • Unlike DISTINCT(), it preserves the original table structure if a table expression is used as the argument.

Use cases:

  • DISTINCT() is preferred when you need to eliminate all duplicate rows or values within a row for further calculations or analysis.

  • VALUES() is particularly useful for situations like:

  • Checking for missing values due to relationship issues with a BLANK value indicator.

  • Creating a distinct list of values for use in other functions like COUNTROWS() or SUMX().

  • Preserving the original table structure and adding a BLANK value for specific scenarios.

Additional differences:

  • Performance: DISTINCT() can be slightly slower than VALUES() when dealing with large datasets.

  • Error handling: DISTINCT() throws an error if the argument is an empty table, while VALUES() returns an empty table in such cases.

Ultimately, the choice between DISTINCT() and VALUES() depends on your specific needs and the desired outcome. Consider the functionality, additional values like BLANK, and performance differences when making your decision.

I hope this explanation clarifies the key differences between DISTINCT() and VALUES() in DAX. Feel free to ask if you have any further questions!

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