backorder Purchase report

Dear All,

Our users are asking for a kind of report where they want to see items ordered in Purchase order but not received.

mean i have created Po for 100 items, now i received 79 items out of it.

i will get grn report for 79 items but at same time i want one more report which tells me that i ordered 100 items and 79 is received and 21 items is not received.

is there any way please help.