Saturday 6 January 2024

List the difference between sum and sumx functions in Power BI?Power BI interview questions and answers 270

List the difference between sum and sumx functions in Power BI?

Here's a breakdown of the key differences between the SUM and SUMX functions in Power BI:


  • Simple aggregation: Sums up values in a single column.

  • Direct calculation: Operates directly on the column without iterating through rows.

  • Example: Total Sales = SUM(Sales[Amount])


  • Iterator function: Iterates through each row of a table to perform a calculation and then sums up the results.

  • Handles expressions: Can use any expression that involves multiple columns or calculations within a row.

  • More versatile: Offers greater flexibility for complex calculations.

  • Example: Total Sales with Discount = SUMX(Sales, Sales[Amount] - Sales[Discount])

Key Differences:








Single column only

Multiple columns/expressions


Direct on a column

Row-by-row calculation


Generally faster

Can be slower for large datasets

Use cases

Simple aggregations

Complex calculations, conditional logic

When to Use Which:

  • Use SUM:

  • When you need to quickly sum up a single column of values.

  • When performance is critical for large datasets.

  • Use SUMX:

  • When you need to perform calculations that involve multiple columns or logic within each row.

  • When you need to apply filters or conditions to rows before summing.

  • When you need to create dynamic calculations that change based on context.

In essence:

  • SUM is for simple, straightforward aggregations.

  • SUMX is for more complex, row-by-row calculations and expressions.

Additional Insights:

  • Iterator functions: SUMX is part of a family of iterator functions in DAX, including AVERAGEX, COUNTX, MINX, MAXX, etc., which all follow a similar row-by-row approach.

  • Performance considerations: While SUMX is powerful, it can be slower than SUM for large datasets due to its iterative nature. Be mindful of performance implications when choosing between them.

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