Thanks for the reply.
I don't know the document no. I'm having two POs. 2nd PO is refer to first one and FRBNR field fill by the first once PO no (That's not standard way. but our company use that bill of lading field as a reference field). Therefore I have all the details of first PO and wanna get the details of 2nd one (which is refer the first one). As you said I can build an alter index if its using frequently. But I need this only one custom report. So I don't feel it's worth to have an index only for this report.
Please let me know if there's any other way that I can refer this field.