One of the most powerful features in Power Pivot is the ability to create relationships between tables and then use the related tables to lookup or filter related data. You retrieve related values from tables by using the formula language provided with Power Pivot, Data Analysis Expressions (DAX). DAX uses a relational model and therefore can easily and accurately retrieve related or corresponding values in another table or column. If you are familiar with VLOOKUP in Excel, this functionality in Power Pivot is similar, but much easier to implement.
You can create formulas that do lookups as part of a calculated column, or as part of a measure for use in a PivotTable or PivotChart. For more information, see the following topics:
Calculated Fields in Power Pivot
Calculated Columns in Power Pivot
This section describes the DAX functions that are provided for lookup, together with some examples of how to use the functions.
Note: Depending on the type of lookup operation or lookup formula you want to use, you might need to create a relationship between the tables first.
Understanding Lookup Functions
The ability to lookup matching or related data from another table is particularly useful in situations where the current table has only an identifier of some kind, but the data you need (such as product price, name, or other detailed values) is stored in a related table. It is also useful when there are multiple rows in another table related to the current row or current value. For example, you can easily retrieve all the sales tied to a particular region, store, or salesperson.
In contrast to Excel lookup functions such as VLOOKUP, which are based on arrays, or LOOKUP, which gets the first of multiple matching values, DAX follows existing relationships among tables joined by keys to get the single related value that matches exactly. DAX can also retrieve a table of records that are related to the current record.
Note: If you are familiar with relational databases, you can think of lookups in Power Pivot as similar to a nested subselect statement in TransactSQL.
Retrieving a Single Related Value
The RELATED function returns a single value from another table related to the current value in the current table. You specify the column that contains the data that you want, and the function follows existing relationships between tables to fetch the value from the specified column in the related table. In some cases, the function must follow a chain of relationships to retrieve the data.
For example, suppose you have a list of today's shipments in Excel. However, the list contains only an employee ID number, an order ID number, and a shipper ID number, making the report hard to read. To get the extra information you want, you can convert that list into a Power Pivot linked table, and then create relationships to the Employee and Reseller tables, matching EmployeeID to the EmployeeKey field, and ResellerID to the ResellerKey field.
To display the lookup information in your linked table, you add two new calculated columns, with the following formulas:
= RELATED('Employees'[EmployeeName])
= RELATED('Resellers'[CompanyName])
Today’s shipments before lookup
OrderID 
EmployeeID 
ResellerID 
100314 
230 
445 
100315 
15 
445 
100316 
76 
108 
Employees table
EmployeeID 
Employee 
Reseller 
230 
Kuppa Vamsi 
Modular Cycle Systems 
15 
Pilar Ackeman 
Modular Cycle Systems 
76 
Kim Ralls 
Associated Bikes 
Today’s shipments with lookups
OrderID 
EmployeeID 
ResellerID 
Employee 
Reseller 
100314 
230 
445 
Kuppa Vamsi 
Modular Cycle Systems 
100315 
15 
445 
Pilar Ackeman 
Modular Cycle Systems 
100316 
76 
108 
Kim Ralls 
Associated Bikes 
The function uses the relationships between the linked table and the Employees and Resellers table to get the correct name for each row in the report. You can also use related values for calculations. For more information and examples, see RELATED Function.
Retrieving a List of Related Values
The RELATEDTABLE function follows an existing relationship, and returns a table that contains all matching rows from the specified table. For example, assume you want to find out how many orders each reseller has placed this year. You could create a new calculated column in the Resellers table that includes the following formula, which looks up records for each reseller in the ResellerSales_USD table, and counts the number of individual orders placed by each reseller. These tables are part of the DAX sample workbook. For more information about sample data, see Get sample data for DAX and Data Model tutorials.
=COUNTROWS(RELATEDTABLE(ResellerSales_USD))
In this formula, the RELATEDTABLE function first gets the value of ResellerKey for each reseller in the current table. (You do not need to specify the ID column anywhere in the formula, because Power Pivot uses the existing relationship between the tables.) The RELATEDTABLE function then gets all the rows from the ResellerSales_USD table that are related to each reseller, and counts the rows. If there is no relationship (direct or indirect) between the two tables, then you will get all rows from the ResellerSales_USD table.
For the reseller Modular Cycle Systems in our sample database, there are four orders in the sales table, so the function returns 4. For Associated Bikes, the reseller has no sales, so the function returns a blank.
Reseller 
Records in sales table for this reseller 

Modular Cycle Systems 
Reseller ID 
SalesOrderNumber 
445 
SO53494 

445 
SO71872 

445 
SO65233 

445 
SO59000 

Reseller ID 
SalesOrderNumber 

Associated Bikes 
Note: Because the RELATEDTABLE function returns a table, not a single value, it must be used as an argument to a function that performs operations on tables. For more information, see RELATEDTABLE Function.