PO Number from Invoice

Hi,

Which is the best way to get a purchase order nunber when you only have the invoice number.

I'm currently running the code below but need to know if there is a better way.

SELECT c.je_header_id,c.je_line_num,po.po_header_id,po.segment1 "po num", b.reference_2 "invoice num",b.reference_1 "vendor"FROM gl_import_references b,gl_je_lines c,GL_JE_HEADERS d,po_headers_all poWHERE c.je_line_num = b.je_line_numAND c.je_header_id = b.je_header_idAND c.je_header_id = d.je_header_id