Join data from two worksheets

Hallo! I am trying to join sales data from 2 worksheets to come up with a compiled report.
Please look at the attachment below to understand my query.

I have 2 Departments selling products to various customers. Some customers are shared between the 2 departments. So far I am only able to come up sales data per department as shown in worksheets Department A and Department B.

I want a combined report that shows data from the 2 departments as shown in the worksheet merged data.

How can I achieve this in Excel 2007?

Thanks.