Extract PO still to be invoiced

HI ALL

We are doing an add-on program which need to extract PO still to be invoice

We select all the PO from EKBE , if GR Qty minus IR Qty is not equal to zero, it will be extracted.

But we have large amount of PO , so this program do not have good performance.

When using ME2N , select RECHNUNG , we can get what we want . Is there any standard function to do this.

Also , I am considering tick EKPO-EREKZ when doing MIRO, but I found once I tick it , it won't be reset to blank even if I cancel the invoice in MR8M.

Can anyone tell me if there any way to improve the performance of this logic.

Thanks a lot.

Danielle