Why RELATED for cross-table values in Power BI? - Purpose & Use Cases

The Big Idea

Discover how to connect your data tables like magic and save hours of manual work!

The Scenario

Imagine you have two separate Excel sheets: one with sales data and another with customer details. To find the customer name for each sale, you have to manually look up and copy the names from one sheet to the other.

The Problem

This manual lookup is slow and prone to mistakes. Copying data between sheets can cause errors, and updating the data means repeating the tedious process all over again.

The Solution

The RELATED function in Power BI automatically fetches matching values from related tables. It links data across tables seamlessly, so you never have to copy or search manually.

Before vs After

✗ Before

VLOOKUP(CustomerID, CustomerTable, 2, FALSE)

✓ After

CustomerName = RELATED(CustomerTable[CustomerName])

What It Enables

It enables you to combine and analyze data from multiple tables effortlessly, creating richer and more accurate reports.

Real Life Example

A sales manager can instantly see customer names next to sales figures without juggling multiple files or manual lookups.

Key Takeaways

Manual cross-table lookups are slow and error-prone.

RELATED automates fetching matching values across tables.

This makes reports faster, cleaner, and easier to update.

Practice

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

easy

A. It creates a new relationship between two tables.

B. It fetches a value from a related table based on existing relationships.

C. It deletes rows from a related table.

D. It aggregates data within the same table.

Solution

1. Step 1: Understand the purpose of RELATED

   The RELATED function is designed to retrieve a value from another table that is connected through a relationship in the data model.

2. Step 2: Differentiate from other functions

   RELATED does not create relationships or delete data; it only fetches values from an existing related table.

3. Final Answer:

   It fetches a value from a related table based on existing relationships. -> Option B

4. Quick Check:

   RELATED fetches related values = A [OK]

Hint: RELATED pulls data from linked tables only [OK]

Common Mistakes:

• Thinking RELATED creates relationships
• Assuming RELATED works without a relationship
• Confusing RELATED with aggregation functions

2. Which of the following is the correct syntax to use RELATED in a calculated column to get the 'CategoryName' from a related 'Product Categories' table?

easy

A. RELATED('Product Categories'[CategoryName])

B. RELATED(Product Categories[CategoryName])

C. RELATED Product Categories[CategoryName]

D. RELATED[Product Categories.CategoryName]

Solution

1. Step 1: Recall correct RELATED syntax

   The RELATED function requires the table name in single quotes if it contains spaces or special characters, followed by the column name in square brackets.

2. Step 2: Check each option

   RELATED('Product Categories'[CategoryName]) uses the correct syntax. Without quotes around the table name with space it fails, missing parentheses fails, and bracket notation is invalid.

3. Final Answer:

   RELATED('Product Categories'[CategoryName]) -> Option A

4. Quick Check:

   RELATED syntax with quotes = B [OK]

Hint: Use single quotes around table names with spaces [OK]

Common Mistakes:

• Omitting quotes around table names
• Using dot notation inside RELATED
• Missing parentheses after RELATED

3. Given two tables: Orders with columns OrderID, ProductID, and Quantity, and Products with columns ProductID and Price. There is a relationship between Orders[ProductID] and Products[ProductID]. What will the following calculated column in Orders return?

OrderValue = Orders[Quantity] * RELATED(Products[Price])

medium

A. The total price for each order line by multiplying quantity with product price.

B. The sum of all product prices in the Products table.

C. The quantity multiplied by the total number of products.

D. An error because RELATED cannot be used in calculated columns.

Solution

1. Step 1: Understand the relationship and calculation

   RELATED fetches the price of the product for each order line by matching ProductID. Multiplying by Quantity gives the total value for that order line.

2. Step 2: Trace the calculation

   The formula computes the total price for each order line row-by-row by multiplying Quantity with the RELATED product Price. It does not aggregate or error out.

3. Final Answer:

   The total price for each order line by multiplying quantity with product price. -> Option A

4. Quick Check:

   Quantity * RELATED(Price) = line total = C [OK]

Hint: RELATED pulls matching row value for each row [OK]

Common Mistakes:

• Thinking RELATED aggregates values
• Assuming RELATED cannot be used in calculated columns
• Confusing multiplication with aggregation

4. You wrote this calculated column in the Sales table:

ProductCategory = RELATED(Product[Category])

But you get an error saying "The column 'Category' either doesn't exist or is not related." What is the most likely cause?

medium

A. The Sales table has duplicate rows causing RELATED to fail.

B. The RELATED function cannot be used in calculated columns.

C. There is no relationship between Sales and Product tables on the relevant keys.

D. The column name 'Category' is misspelled in the Product table.

Solution

1. Step 1: Analyze the error message

   The error indicates that RELATED cannot find a related row, usually because the tables are not connected by a relationship.

2. Step 2: Check other possibilities

   RELATED can be used in calculated columns. Misspelling would cause a different error, and duplicates don't cause this error.

3. Final Answer:

   There is no relationship between Sales and Product tables on the relevant keys. -> Option C

4. Quick Check:

   RELATED needs relationships = D [OK]

Hint: Check relationships if RELATED gives column not found error [OK]

Common Mistakes:

• Assuming RELATED works without relationships
• Ignoring spelling errors in column names
• Blaming data duplicates for RELATED errors

5. You have three tables: Sales (with ProductID and Quantity), Products (with ProductID, CategoryID, and CategoryName), and Categories (with CategoryID and CategoryName).

You want to create a calculated column in Sales that shows the CategoryName for each sale. Which DAX formula correctly uses RELATED to get this value?

hard

A. RELATED(Categories[CategoryName])

B. RELATED(RELATED(Categories[CategoryName]))

C. RELATED(Products[CategoryID]) & RELATED(Categories[CategoryName])

D. RELATED(Products[CategoryName])

Solution

1. Step 1: Understand the relationships

   Sales is related to Products by ProductID, and Products is related to Categories by CategoryID. Products contains CategoryName (likely via its own RELATED to Categories).

2. Step 2: Use RELATED with the correct direct relationship

   RELATED(Products[CategoryName]) fetches from the directly related Products table.

3. Step 3: Rule out others

   A targets an indirectly related table, C uses invalid concatenation on unrelated data, D has invalid syntax.

4. Final Answer:

   RELATED(Products[CategoryName]) -> Option D

5. Quick Check:

   RELATED fetches from directly related table = B [OK]

Hint: RELATED only fetches from directly related tables [OK]

Common Mistakes:

• Trying to chain RELATED calls
• Using RELATED on unrelated tables
• Assuming RELATED can fetch through multiple tables automatically