SSRS Lookup functions allow you to combine data from two datasets in a single data region.
There are different types of lookup functions:
The Lookup function is used for an 1-1 relation between two dataset.
The LookupSet function is used for an 1-N relation between two dataset:
Usually, LookupSet is combined with Join() function:
Lookup and LookupSet example
In this example, the lookup function join the Products Dataset and the Suppliers dataset using the SupplierID:
The column Vendor is calculated using this expression:
The MultiLookup function is used for an N-N relation between two dataset:
The difference between previous functions is that Fields!datasetA_IDs.Value is an array of values.
Usually, we can use the Split() function to convert delimiteted strings to a list of value: