This post explains the concept of below DAX functions
I need to explain the data modelling little bit before going to DAX functions. As you know, we need to create a relationship either manually or automatically to use the tables together to get the expected result.
We have 3 different relationships available.
In the context, let us consider a one-to-many relationship. If you have CUSTOMER master and FACT tables then trying to create a relationship, then that would create a one-to-many relationship.
It means we have unique records on the customer table but multiple same values on the FACT table with reference to the connected columns.
If you want to create a new calculated column on the CUSTOMER table then you need to use RELATEDTABLE DAX function. On the other hand, when you want to create a calculated column on the FACT table then you need to use the RELATED function.
Customer First Purchase = MINX(
‘Sale'[Invoice Date Key])
State = RELATED(‘City'[State Province])