Query to get the XML Tags

 SELECT DBMS_XMLGEN.getxml(

'SELECT ooha.order_number
     , oola.line_number so_line_number
     , oola.ordered_item
     , oola.ordered_quantity * oola.unit_selling_price so_extended_price
     , rcta.trx_number invoice_number
     , rcta.trx_date
     , rctla.line_number inv_line_number
     , rctla.unit_selling_price inv_unit_selling_price
FROM   oe_order_headers_all ooha
     , oe_order_lines_all oola
     , ra_customer_trx_all rcta
     , ra_customer_trx_lines_all rctla
WHERE  ooha.header_id = oola.header_id
AND    rcta.customer_trx_id = rctla.customer_trx_id
AND    rctla.interface_line_attribute6 = TO_CHAR (oola.line_id)
AND    rctla.interface_line_attribute1 = TO_CHAR (ooha.order_number)
AND    order_number = &p_order_number')
FROM DUAL