TOPN function in Power BI - Cell-by-Cell Formula Trace

Sample Data

This table shows products and their sales amounts.

Cell	Value
A1	Product
B1	Sales
A2	Apple
B2	150
A3	Banana
B3	120
A4	Cherry
B4	180
A5	Date
B5	90
A6	Elderberry
B6	200

Formula Trace

TOPN(3, Table, Table[Sales], DESC)

Step 1: Table with columns Product and Sales

Step 2: Sort Table by Sales descending

Step 3: Take top 3 rows from sorted table

Cell Reference Map

    A        B
1 Product  Sales
2 Apple    150
3 Banana   120
4 Cherry   180
5 Date      90
6 Elderberry 200

Arrows:
Table[Sales] -> Used for sorting in TOPN

The formula uses the Sales column (B2:B6) to sort the table and pick the top 3 products.

Result

    A          B
1 Product    Sales
2 Elderberry 200
3 Cherry     180
4 Apple      150

The result shows the top 3 products with the highest sales values.

Sheet Trace Quiz - 3 Questions

What does the TOPN function do in this example?

A Returns all products sorted alphabetically

B Returns the 3 products with the highest sales

C Returns the 3 products with the lowest sales

D Returns the total sales for all products

Key Result

TOPN(N, Table, Table[Column], DESC) returns top N rows sorted by Column descending

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