Returns the first matching value for the specified name from a dataset that contains name/value pairs.
Use Lookup to retrieve the value from the specified dataset for a name/value pair where there is a 1-to-1 relationship. For example, for an ID field in a table, you can use Lookup to retrieve the corresponding Name field from a dataset that is not bound to the data region.
Lookup 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.
On the first match of source expression and destination expression, evaluates the result expression for that row in the dataset.
Returns the result expression value.
The following restrictions apply:
Lookup 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. The return type is the same as the data type of the evaluated result expression.
Source, destination, and result expressions cannot include references to report or group variables.
Lookup 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.
The Report.Language property.
In the following example, assume that a table is bound to a dataset that includes a field for the product identifier ProductID. A separate dataset called "Product" contains the corresponding product identifier ID and the product name Name.
In the following expression, Lookup compares the value of ProductID to ID in each row of the dataset called "Product" and, when a match is found, returns the value of the Name field for that row.
=Lookup(Fields!ProductID.Value, Fields!ID.Value, Fields!Name.Value, "Product")