Report Builder functions - Multilookup 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 first-match values for the specified set of names 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
Multilookup(source_expression, destination_expression, result_expression, dataset)
Parameters
source_expression
(VariantArray) An expression that is evaluated in the current scope and that specifies the set of names or keys to look up. For example, for a multivalue parameter, =Parameters!IDs.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!ID.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!Name.Value.
dataset
A constant that specifies the name of a dataset in the report. For example, "Colors".
Return
Returns a VariantArray, or Nothing if there is no match.
Remarks
Use Multilookup to retrieve a set of values from a dataset for name-value pairs where each pair has a 1-to-1 relationship. MultiLookup is the equivalent of calling Lookup for a set of names or keys. For example, for a multivalue parameter that is based on primary key identifiers, you can use Multilookup in an expression in a text box in a table to retrieve associated values from a dataset that is not bound to the parameter or to the table.
Multilookup does the following:
Evaluates the source expression in the current scope and generates an array of variant objects.
For each object in the array, calls Lookup Function (Report Builder and SSRS) and adds the result to the return array.
Returns the set of results.
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 retrieve multiple values from a dataset with name-value pairs for a name where there is a 1-to-many relationship, use LookupSet Function (Report Builder and SSRS).
The following restrictions apply:
Multilookup is evaluated after all filter expressions are applied
Only one level of look-up 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.
Multilookup 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
A. Use MultiLookup function
Assume a dataset called "Category" contains the field CategoryList, which is a field that contains a comma-separated list of category identifiers, for example, "2, 4, 2, 1".
The dataset CategoryNames contains the category identifier and category name, as shown in the following table.
| ID | Name |
|---|---|
| 1 | Accessories |
| 2 | Bikes |
| 3 | Clothing |
| 4 | Components |
To look up the names that correspond to the list of identifiers, use Multilookup. You must first split the list into a string array, call Multilookup to retrieve the category names, and concatenate the results into a string.
The following expression, when placed in a text box in a data region bound to the Category dataset, displays "Bikes, Components, Bikes, Accessories":
=Join(MultiLookup(Split(Fields!CategoryList.Value,","),
Fields!CategoryID.Value,Fields!CategoryName.Value,"Category")),
", ")
B. Use MultiLookup with multivalue parameter
Assume a dataset ProductColors contains a color identifier field ColorID and a color value field Color, as shown in the following table.
| ColorID | Color |
|---|---|
| 1 | Red |
| 2 | Blue |
| 3 | Green |
Assume the multivalue parameter MyColors is not bound to a dataset for its available values. The default values for the parameter are set to 2 and 3. The following expression, when placed in a text box in a table, concatenates the multiple selected values for the parameter into a comma-separated list and displays "Blue, Green".
=Join(MultiLookup(Parameters!MyColors.Value,Fields!ColorID.Value,Fields!Color.Value,"ProductColors"),", ")