RELATED function is a Power BI Relationship function in DAX which returns a related value from another table.
The RELATED function requires that a relationship exists between the current table and the table with related information.
If a relationship does not exist, you must create a relationship.
RELATED function requires the column that contains the data that you want, and the function follows an existing many-to-one relationship to fetch the value from the specified column in the related table.
SYNTAX
RELATED(<column>)
column is the column that contains the values you want to retrieve.
Lets look at an example demonstrating a RELATED function in Power BI.
As you can see, Here we have a two tables named as Item and SalesDetails.
There is a relationship(one to many) exists between these table, and the column name is ItemId.
Lets Look at the data in these tables. As you can see the SalesDetails table contains the ItemId, SalesPerson, and total sold quantity details while Item table contains the ItemId, Item Name and their Price.
Lets use the RELATED function to fetch the price details to SalesDetails table for each Item.
For this we will create a calculated column in table SalesDetails, as you can use related function only on the many side of relationship as shown below.
Right click on table SalesDetails then click on new column.
Now create the following DAX expression named Price that uses RELATED function.
You will notice that as soon you start writing a syntax for related function, it gives you suggestion that which column you want from the related table, as you can see it suggests all the columns from Item table.
As you want to fetch the Price so select Price from suggested Item table, and commit the DAX.
Price = RELATED('Item'[Price])
Once you commit the Dax, a calculated column is created in SalesDetails table as shown below.
Lets quickly verify to ensure that it fetches the price from Item table in table SalesDetails.
Go to Data view, and you can see now Price column in table SalesDetails contains the Price against each Item.
Using RELATED Function in Measure
Lets say you want to display the total sales done by SalesPerson that would be a Total SalesAmount = Total Quantity * Total Price
Lets create a measure named TotalSalesAmount in SalesDetails table.
TotalSalesAmount = SUMX ( SalesDetails, RELATED ( 'Item'[Price] ) * SalesDetails[Quantity])
After commit the DAX, Lets drag the measure TotalSalesAmount into table visual.
You can see, it returns the total sales amount done by Sales Person.
The RELATED function requires that a relationship exists between the current table and the table with related information.
Lets see, if there is no relationship between table Item and SalesDetails as shown below.
Now when you try to use Related function then you will get following error.
