Lookup functions in SSRS 2008 R2 - II

 Introduction

In my last post on Lookup functions related to SSRS 2008 R2, I had explained Lookup(). It is used to fetch the first matching value from the other DataSet. Now, what if we want all the matching values from the other DataSet. Here, the LookupSet() function comes handy. Let’s try to understand this.

Syntax

LookupSet(source_expression, destination_expression, result_expression, dataset)

source_expression – The field which will act as the key/lookup value for the destination. This will be evaluated in the current scope – generally the DataSet with which the Tablix is bound.

destination_expression – The field in which the source expression will be looked in. This field will belong to the dataset provided in the same function as the last parameter. 

result_expression – The field we want to retrieve from the destination DataSet for the matching source_expression & destination_expression for each row. 

Note, If multiple matches are found, all the values from the matching rows will be returned. And we can not use any aggregate functions in the result_expression.

Dataset – The Dataset in which we want to look the values into.

Returns – A VariantArray, or Nothing if there is no match.

Example

Continuing with the same example from the last post of Employees & Departments, suppose we want to display the name of all the departments to which the Employee is related to, we can use the following expression -

=JOIN(LookupSet(Fields!DepartmentID.Value, Fields!ID.Value, Fields!Name.Value, "Departments"),",")

Here, we have used 2 functions of SSRS,

1. LookupSet() – To get an Variant array of the matching values. Here, the DepartmentID field will be matched with the ID field of the Departments Dataset and the Name from all the matching rows will be returned.
   
2. JOIN() – To join all the elements of the array as a comma separated string.

Hope, I have explained clearly the use of LookupSet() funciton. Next, I will blog about the last Lookup function – MultiLookup().