TOPN function in Power BI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the TOPN function do in Power BI?

The TOPN function returns the top N rows of a table based on a specified expression or column, sorted in descending order by default.

beginner

Write the basic syntax of the TOPN function.

TOPN(<N_value>, <table>, <orderBy_expression>[, <order>[, <orderBy_expression>[, <order>]...]]), where N_value is how many rows to return.

intermediate

How can you change the sorting order in TOPN from descending to ascending?

Add the optional <order> argument with the value ASC after the <orderBy_expression> to sort ascending instead of the default DESC.

beginner

What type of value does the TOPN function return?

TOPN returns a table containing the top N rows based on the sorting criteria, not a single value.

intermediate

Can TOPN be used inside other DAX functions? Give an example.

Yes, for example, you can use TOPN inside CALCULATE to filter a table to the top N rows before aggregation.

What does the TOPN function return in Power BI?

A A table with the top N rows

B A single numeric value

C A text string

D A Boolean value

TOPN returns a table containing the top N rows based on the sorting criteria.

Which argument in TOPN specifies how many rows to return?

A <N_value>

B <orderBy_expression>

C <table>

D <order>

is the number of rows TOPN will return.

How do you sort the TOPN results in ascending order?

A TOPN always sorts ascending by default

B Add DESC after the orderBy_expression

C Use the SORT function instead

D Add ASC after the orderBy_expression

Adding ASC after the orderBy_expression changes the sort order to ascending.

Can TOPN be used inside CALCULATE to filter data?

A No, TOPN cannot be nested

B Yes, to filter to top N rows before aggregation

C Only with numeric columns

D Only in Power Query, not DAX

TOPN can be nested inside CALCULATE to filter data to top N rows.

What is the default sort order of TOPN if not specified?

A Random

B Ascending

C Descending

D Alphabetical

TOPN sorts in descending order by default.

Explain how the TOPN function works and when you might use it in a Power BI report.

Think about showing best-selling products or top customers.

Describe how to change the sorting order in TOPN and why that might be useful.

Consider when you want to see smallest sales instead of largest.

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