Optimizing DAX queries in Power BI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main goal of optimizing DAX queries?

To make DAX calculations run faster and use less memory, improving report performance and user experience.

intermediate

Why should you avoid using 'FILTER' on large tables in DAX?

Because 'FILTER' scans the entire table row by row, which can slow down queries on big datasets.

beginner

How does using variables (VAR) help optimize DAX queries?

Variables store intermediate results so calculations are done once, reducing repeated work and speeding up queries.

intermediate

What is the benefit of using CALCULATE with simple filters instead of complex FILTER expressions?

CALCULATE with simple filters lets the engine use optimized storage indexes, making queries faster than complex row-by-row filters.

beginner

Why is it important to reduce the number of columns in your data model for DAX performance?

Fewer columns mean less data to scan and store, which speeds up calculations and reduces memory use.

Which DAX function is generally faster for filtering large tables?

A CALCULATE with simple filters

B FILTER with complex conditions

C SUMX over entire table

D ALL to remove filters

CALCULATE with simple filters uses optimized engine paths, making it faster than FILTER on large tables.

What does using VAR in a DAX measure help you avoid?

A Data refresh

B Changing data types

C Data import errors

D Repeated calculations

VAR stores a value once so it can be reused, avoiding repeated calculations.

Which practice improves DAX query speed the most?

A Reducing columns in the data model

B Adding more calculated columns

C Using many nested FILTER functions

D Using complex IF statements

Reducing columns reduces data size and speeds up calculations.

What is a downside of using FILTER on large tables?

A It disables relationships

B It scans every row, slowing performance

C It deletes data

D It changes data types

FILTER evaluates each row, which can be slow on big tables.

How can you check which DAX queries are slow in Power BI?

A Restart Power BI Desktop

B Use Excel formulas

C Use Performance Analyzer tool

D Change report theme

Performance Analyzer shows query times and helps identify slow DAX.

Explain three ways to optimize DAX queries for better performance.

Think about filtering, reusing calculations, and data size.

Describe why FILTER can slow down DAX queries and how to avoid it.

Consider how row-by-row operations affect speed.