Report to list Purchase Requisitions

Hi Gurus,

Here is my scenario:

If I have 3 POs created w.r.t PR 123(total value = 10qty*2USD = 20.00 USD).

PO1 created with total value 10.00USD (5qty*2USD)

PO2 created with total value 6.00USD (3qty*2USD)

PO3 created with total value 5.00USD (2qty*2.5USD), but the PR total open value now is only 4.00USD.

My requirement is to have a report to get all the PR with total open value not equal to the total value of POs created w.r.t PR, in the above case the PR123 with PO3 will displayed in the report. How should I do? Is there's any field in PR table which keeps the total open value?

Thanks a lot.