🚀 Data Analyst Roadmap — Part 25

📊 Power BI Level 4 — DAX Fundamentals: Measures, Calculated Columns & Filter Context

Now that you understand Power Query and Data Modeling, it's time to learn one of the most important parts of Power BI:

DAX — Data Analysis Expressions

DAX is the formula language used in Power BI to create calculations.

🔹 1. What Is DAX?

DAX is used to create:

• Measures

• Calculated columns

• Calculated tables

For example:

Total Sales = SUM(Sales[Sales_Amount])

This simple measure can become the foundation for many Power BI reports.

🔹 2. Measures vs Calculated Columns

This is one of the most common Power BI interview questions.

•

Calculated Column: Calculates a value for each row.

• Example: Profit = Sales[Sales_Amount] - Sales[Cost]

• If there are 1 million rows, the column contains a result for each row.

•

Measure: Calculates a result when it is used in a visual.

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

• A measure can change depending on the filters and selections in the report.

🔹 3. Simple Example

Suppose your Sales table contains:

• Product: Laptop | Sales: 80,000 | Cost: 60,000

• Product: Mouse | Sales: 2,000 | Cost: 1,000

•

Product: Keyboard | Sales: 4,000 | Cost: 2,500

•

Calculated column: Profit = Sales[Sales] - Sales[Cost]

calculates profit for every row.

•

Measure: Total Profit = SUM(Sales[Sales]) - SUM(Sales[Cost])

calculates the total based on the current filter context.

🔹 4. Basic Aggregation Functions

Some DAX functions you'll use constantly are:

• SUM(), AVERAGE(), MIN(), MAX(), COUNT(), COUNTROWS(), DISTINCTCOUNT()

Examples:

• Total Sales = SUM(Sales[Sales])

• Average Sales = AVERAGE(Sales[Sales])

• Total Orders = COUNTROWS(Sales)

• Total Customers = DISTINCTCOUNT(Sales[Customer_ID])

🔹 5. Why DISTINCTCOUNT() Matters

Suppose the same customer placed 10 orders.

COUNT() could count all transaction rows. But DISTINCTCOUNT(Sales[Customer_ID]) counts the customer only once.

So if you want "How many unique customers do we have?"

DISTINCTCOUNT() is often the right choice.

🔹 6. Creating Your First Measure

In Power BI: Modeling → New Measure

Then write:

Total Sales = SUM(Sales[Sales_Amount])

You can then drag Total Sales into a Card visual. Result might show:

TOTAL SALES ₹12.5 Cr

🔹 7. Measures Respond to Filters

This is where DAX becomes powerful.

Suppose your report contains Total Sales = ₹10 Crore. Now select Region = West. The same measure Total Sales = SUM(Sales[Sales_Amount]) may now show ₹3 Crore.

You didn't create another measure. The filter changed the calculation. This is called Filter Context.

🔹 8. What Is Filter Context?

Filter context means: The filters currently affecting a DAX calculation.

Filters can come from:

• Slicers, Visuals, Rows and columns, Page filters, Report filters, Relationships, DAX expressions

For example: Region = West, Year = 2026, Category = Electronics. The Total Sales measure calculates only within that context.

🔹 9. A Simple Way to Understand Filter Context

Think of it like this:

• Total Sales → Which rows are currently visible? → Apply filters → Calculate SUM

This concept is extremely important.