TOPN function in Power BI - Real Business Scenario

Scenario Mode

👤 Your Role: You are a sales analyst at a retail company.

📋 Request: Your manager wants to see the top 3 products by total sales amount for the last quarter to focus marketing efforts.

📊 Data: You have sales data including Product Name, Sales Date, Quantity Sold, and Sales Amount.

🎯 Deliverable: Create a report showing the top 3 products by total sales amount for the last quarter with their sales figures.

Sample Data

Product Name	Sales Date	Quantity Sold	Sales Amount
Alpha	2024-01-15	10	500
Beta	2024-02-10	5	300
Gamma	2024-03-05	8	400
Alpha	2024-03-20	7	350
Beta	2024-01-25	6	360
Delta	2024-02-15	4	200
Gamma	2024-01-30	3	150
Alpha	2024-02-05	9	450
Delta	2024-03-10	5	250
Beta	2024-03-25	7	420

1

Step 1: Filter the sales data to include only sales from the last quarter (January to March 2024).

Use a date filter on Sales Date column for dates between 2024-01-01 and 2024-03-31.

Expected Result

Filtered data contains only sales records from Q1 2024.

2

Step 2: Create a measure to calculate total sales amount per product.

Total Sales = SUM('Sales'[Sales Amount])

Expected Result

Measure sums sales amounts for each product.

3

Step 3: Use the TOPN function to find the top 3 products by total sales amount.

Top 3 Products = TOPN(3, SUMMARIZE('Sales', 'Sales'[Product Name], "TotalSales", [Total Sales]), [TotalSales], DESC)

Expected Result

A table with the top 3 products and their total sales amounts.

4

Step 4: Create a table visual in Power BI with Product Name and Total Sales from the Top 3 Products measure.

Add a table visual with columns: Product Name, Total Sales using the Top 3 Products table.

Expected Result

Table shows top 3 products with their total sales amounts.

Final Result

Top 3 Products by Sales (Q1 2024)
+-------------+-------------+
| Product Name| Total Sales |
+-------------+-------------+
| Alpha       | 1300        |
| Beta        | 1080        |
| Gamma       | 550         |
+-------------+-------------+

✓Alpha is the top-selling product with total sales of 1300.

✓Beta is the second top product with total sales of 1080.

✓Gamma ranks third with total sales of 550.

✓Delta is not in the top 3 for this quarter.

Bonus Challenge

Create a dynamic slicer to select any quarter and show the top 3 products for the selected quarter.

Show Hint

Use a Date table with quarters and modify the TOPN measure to filter based on the selected quarter from the slicer.

Practice

1. What does the TOPN function do in Power BI?

easy

A. Joins two tables based on a key column.

B. Calculates the sum of a column in a table.

C. Filters rows where a condition is true.

D. Returns the top N rows from a table based on a specified column's values.

Solution

1. Step 1: Understand the purpose of TOPN

   TOPN is designed to return a subset of rows from a table, specifically the top N rows sorted by a column.

2. Step 2: Compare with other functions

   Functions like SUM aggregate values, FILTER filters rows by condition, and JOIN merges tables. TOPN specifically returns top rows.

3. Final Answer:

   Returns the top N rows from a table based on a specified column's values. -> Option D

4. Quick Check:

   TOPN = returns top rows [OK]

Hint: TOPN picks top rows by sorting a column [OK]

Common Mistakes:

• Confusing TOPN with aggregation functions like SUM
• Thinking TOPN filters by condition instead of top values
• Mixing TOPN with table joins

2. Which of the following is the correct syntax for the TOPN function in DAX?

easy

A. TOPN(<number_of_rows>, <table>, <order_by_column>, <order>)

B. TOPN(<table>, <number_of_rows>, <order_by_column>, <order>)

C. TOPN(<number_of_rows>, <order_by_column>, <table>, <order>)

D. TOPN(<order_by_column>, <number_of_rows>, <table>, <order>)

Solution

1. Step 1: Recall TOPN function syntax

   The correct syntax is TOPN(number_of_rows, table, order_by_column, order). The first argument is how many rows to return.

2. Step 2: Verify argument order

   Number of rows comes first, then the table, then the column to sort by, and finally the sort order (ASC or DESC).

3. Final Answer:

   TOPN(<number_of_rows>, <table>, <order_by_column>, <order>) -> Option A

4. Quick Check:

   Syntax = TOPN(number_of_rows, table, column, order) [OK]

Hint: Number of rows is always first in TOPN syntax [OK]

Common Mistakes:

• Swapping table and number_of_rows arguments
• Placing order_by_column before table
• Omitting the order argument

3. Given the table Sales with columns Product and Revenue, what does this DAX expression return?

TOPN(2, Sales, Sales[Revenue], DESC)

medium

A. The two products with the highest revenue.

B. The two products with the lowest revenue.

C. All products sorted by revenue descending.

D. An error because TOPN needs ASC order.

Solution

1. Step 1: Analyze the TOPN parameters

   TOPN(2, Sales, Sales[Revenue], DESC) means return 2 rows from Sales table sorted by Revenue in descending order.

2. Step 2: Understand sorting order effect

   Descending order means highest values come first, so it returns top 2 products with highest revenue.

3. Final Answer:

   The two products with the highest revenue. -> Option A

4. Quick Check:

   TOPN with DESC = top highest values [OK]

Hint: DESC means highest values first in TOPN [OK]

Common Mistakes:

• Confusing DESC with ASC order
• Thinking TOPN returns all rows sorted
• Assuming TOPN returns lowest values by default

4. Identify the error in this DAX expression:

TOPN(3, Sales)

medium

A. Table name should be in quotes.

B. The number of rows should be last argument.

C. Missing the order_by_column argument.

D. Revenue column cannot be used in TOPN.

Solution

1. Step 1: Check TOPN function arguments

   TOPN requires (at minimum) three arguments: number_of_rows, table, order_by_column [, order (ASC or DESC)].

2. Step 2: Identify missing argument

   The expression lacks the order_by_column argument, which is mandatory to specify the column for sorting.

3. Final Answer:

   Missing the order_by_column argument. -> Option C

4. Quick Check:

   TOPN needs order_by_column [OK]

Hint: Always include order_by_column in TOPN [OK]

Common Mistakes:

• Omitting order_by_column argument
• Putting number_of_rows last
• Using quotes around table names

5. You want to create a measure that shows the total revenue of the top 3 products by revenue. Which DAX expression correctly uses TOPN to achieve this?

hard

A. CALCULATE(SUM(Sales[Revenue]), TOPN(3, Sales, DESC))

B. SUMX(TOPN(3, Sales, Sales[Revenue], DESC), Sales[Revenue])

C. SUMX(FILTER(Sales, Sales[Revenue] >= TOPN(3, Sales, Sales[Revenue], DESC)), Sales[Revenue])

D. CALCULATE(TOPN(3, Sales, Sales[Revenue], DESC), SUM(Sales[Revenue]))

Solution

1. Step 1: Understand the goal

   You want to sum revenue only for the top 3 products by revenue.

2. Step 2: Analyze each option

   CALCULATE(SUM(Sales[Revenue]), TOPN(3, Sales, DESC)) has invalid TOPN syntax (missing order_by_column). SUMX(TOPN(3, Sales, Sales[Revenue], DESC), Sales[Revenue]) uses SUMX over TOPN table, correctly summing revenue of top 3 rows. SUMX(FILTER(Sales, Sales[Revenue] >= TOPN(3, Sales, Sales[Revenue], DESC)), Sales[Revenue]) misuses FILTER with TOPN inside condition, which is invalid. CALCULATE(TOPN(3, Sales, Sales[Revenue], DESC), SUM(Sales[Revenue])) misplaces SUM inside CALCULATE with TOPN, causing syntax error.

3. Final Answer:

   SUMX(TOPN(3, Sales, Sales[Revenue], DESC), Sales[Revenue]) -> Option B

4. Quick Check:

   SUMX over TOPN table sums top rows [OK]

Hint: Use SUMX over TOPN to sum top rows [OK]

Common Mistakes:

• Using TOPN directly inside CALCULATE filter
• Misusing FILTER with TOPN in condition
• Putting aggregation inside CALCULATE incorrectly