Report Builder functions - LookupSet function in a paginated report (Report Builder)
Applies to: 
Microsoft Report Builder (SSRS)
Power BI Report Builder
Report Designer in SQL Server Data Tools
Returns the set of matching values for the specified name from a dataset that contains name/value pairs in a paginated report.
Note
You can create and modify paginated report definition (.rdl) files in Microsoft Report Builder, Power BI Report Builder, and in Report Designer in SQL Server Data Tools.
Syntax
LookupSet(source_expression, destination_expression, result_expression, dataset)
Parameters
source_expression
(Variant) An expression that is evaluated in the current scope and that specifies the name or key to look up. For example, =Fields!ID.Value.
destination_expression
(Variant) An expression that is evaluated for each row in a dataset and that specifies the name or key to match on. For example, =Fields!CustomerID.Value.
result_expression
(Variant) An expression that is evaluated for the row in the dataset where source_expression = destination_expression, and that specifies the value to retrieve. For example, =Fields!PhoneNumber.Value.
dataset
A constant that specifies the name of a dataset in the report. For example, "ContactInformation".
Return
Returns a VariantArray, or Nothing if there is no match.
Remarks
Use LookupSet to retrieve a set of values from the specified dataset for a name/value pair where there is a 1-to-many relationship. For example, for a customer identifier in a table, you can use LookupSet to retrieve all the associated phone numbers for that customer from a dataset that is not bound to the data region.
LookupSet does the following:
Evaluates the source expression in the current scope.
Evaluates the destination expression for each row of the specified dataset after filters have been applied, based on the collation of the specified dataset.
For each match of source expression and destination expression, evaluates the result expression for that row in the dataset.
Returns the set of result expression values.
To retrieve a single value from a dataset with name/value pairs for a specified name where there is a 1-to-1 relationship, use Lookup Function (Report Builder and SSRS). To call Lookup for a set of values, use Multilookup Function (Report Builder and SSRS).
The following restrictions apply:
LookupSet is evaluated after all filter expressions are applied.
Only one level of lookup is supported. A source, destination, or result expression cannot include a reference to a lookup function.
Source and destination expressions must evaluate to the same data type.
Source, destination, and result expressions cannot include references to report or group variables.
LookupSet cannot be used as an expression for the following report items:
Dynamic connection strings for a data source.
Calculated fields in a dataset.
Query parameters in a dataset.
Filters in a dataset.
Report parameters.
The Report.Language property.
For more information, see Aggregate Functions Reference (Report Builder and SSRS) and Expression Scope for Totals, Aggregates, and Built-in Collections (Report Builder and SSRS).
Examples
In the following examples, assume the table is bound to a dataset that includes a sales territory identifier TerritoryGroupID. A separate dataset called "Stores" contains the list of all stores in a territory and includes the territory identifier ID and the name of the store StoreName.
A. Use LookupSet
In the following expression, LookupSet compares the value TerritoryGroupID to ID for each row in the dataset called "Stores". For each match, the value of the StoreName field for that row is added to the result set.
=LookupSet(Fields!TerritoryGroupID.Value, Fields!ID.Value, Fields!StoreName.Value, "Stores")
B. Use Join to create a result list
Because LookupSet returns a collection of objects, you cannot display the result expression directly in a text box. You can concatenate the value of each object in the collection as a string.
Use the Visual Basic function Join create a delimited string from a set of objects. Use a comma as a separator to combine the objects in a single line. In some renderers, you might use a Visual Basic line feed (vbCrLF) as a separator to list each value on a new line.
The following expression, when it is used as the Value property for a text box, uses Join to create a list.
=Join(LookupSet(Fields!TerritoryGroupID.Value, Fields!ID.Value, Fields!StoreName.Value, "Stores"),",")
C. Add code to generate HTML
For text boxes that only render a few times, you might choose to add custom code to generate HTML to display values in a text box. HTML in a text box requires extra processing, so this would not be a good choice for a text box that is rendered thousands of times.
Copy the following Visual Basic functions to a Code block in a report definition. MakeList takes the object array that is returned in result_expression and builds an unordered list by using HTML tags. Length returns the number of items in the object array.
Function MakeList(ByVal items As Object()) As String
If items Is Nothing Then
Return Nothing
End If
Dim builder As System.Text.StringBuilder =
New System.Text.StringBuilder()
builder.Append("<ul>")
For Each item As Object In items
builder.Append("<li>")
builder.Append(item)
Next
builder.Append("</ul>")
Return builder.ToString()
End Function
Function Length(ByVal items as Object()) as Integer
If items is Nothing Then
Return 0
End If
Return items.Length
End Function
D. Call the function
To generate the HTML, you must call the function. Paste the following expression in the Value property for the text box and set the markup type for text to HTML. For more information, see Add HTML into a Report (Report Builder and SSRS).
=Code.MakeList(LookupSet(Fields!TerritoryGroupID.Value, Fields!ID.Value, Fields!StoreName.Value, "Stores"))