How To Extract Duplicate Data from a Source Excel/CSV File in SSIS

Scenario: The source excel/csv file must have unique case numbers.Since the alphanumeric case numbers are not auto generated there can be duplicate case numbers with different details.

Requirement: The SSIS package has to identify the duplicate case numbers and load their details in a separate destination file 

Case 1: Only the duplicate Case_numbers are required

 SSIS Package Transformation: Aggregate

 SSIS Package Transformation: Conditional Split

Destination File with Duplicate Case Numbers

Case 2: Duplicate Case_numbers with details are required

 The SSIS package will be different from the previous one.
Additional data transformations Multicast,Sort,Merge Join will be used.

Merge Join transformation will use a left inner join and extract details from master file for the matching data from conditional split transformation

Sort transformation is required for both input sources of merge join.
After execution of the package the destination file has all the details for duplicate case numbers

The important question here is why did I use a merge join  over a cache transform & lookup approach?

A cache transform & lookup approach uses a equi-join and is followed if for each input row there exists a single row in the lookup/cache reference.It returns back the first found matching row.
In our case there were multiple rows for the same case numbers.When lookup is used the destination file looks like as below which is not the desired output.