TOPN function in Power BI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the top 5 products by sales amount.

Power BI

TopProducts = TOPN([1], Sales, Sales[Amount], DESC)

Drag options to blanks, or click blank then click option'

A5

B10

C3

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 10 instead of 5 returns too many products.

Leaving the number blank causes an error.

The TOPN function needs the number of items to return as the first argument. Here, 5 returns the top 5 products.

2fill in blank

medium

Complete the code to return the top 3 customers by total sales.

Power BI

TopCustomers = TOPN([1], Customers, Customers[TotalSales], DESC)

Drag options to blanks, or click blank then click option'

A5

B1

C3

D7

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 returns only the top customer, not top three.

Using 5 or 7 returns more than needed.

To get the top 3 customers, the first argument of TOPN should be 3.

3fill in blank

hard

Fix the error in the TOPN function to correctly return the top 4 products by quantity sold.

Power BI

TopProductsByQty = TOPN([1], Products, Products[Quantity], DESC)

Drag options to blanks, or click blank then click option'

AProducts

BQuantity

CSUM

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using a column name instead of a number causes an error.

Using an aggregation function like SUM in the first argument is incorrect.

The first argument must be a number indicating how many rows to return. Here, 4 is correct.

4fill in blank

hard

Fill both blanks to return the top 3 salespersons by total sales amount in descending order.

Power BI

TopSalespersons = TOPN([1], Salespersons, Salespersons[[2]], DESC)

Drag options to blanks, or click blank then click option'

A3

BAmount

CTotalSales

DSales

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong column names causes errors.

Using a wrong number for top rows returns incorrect results.

The first blank is the number of top rows, 3. The second blank is the column to sort by, TotalSales.

5fill in blank

hard

Fill all three blanks to return the top 5 products by sales amount sorted in descending order.

Power BI

TopProducts = TOPN([1], Products, Products[[2]], [3])

Drag options to blanks, or click blank then click option'

A5

BAmount

CDESC

DASC

Attempts:

3 left

💡 Hint

Common Mistakes

Using ASC instead of DESC returns lowest values.

Using wrong column names causes errors.

The first blank is 5 for top five products, second blank is Amount column, third blank is DESC for descending order.

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