On order Quantity

SELECT sum(pl.quantity)
            FROM po_line_locations_all pll,
                 po_lines_all pl,
                 po_headers_all ph
           WHERE pl.po_header_id = ph.po_header_id
             AND pll.po_line_id = pl.po_line_id
             AND msi.organization_id = pll.ship_to_organization_id
             AND msi.inventory_item_id = pl.item_id