/*

(Q9) List the number of items auctioned each month in 1999 for which data is available, ordered by month. 

*/

import match as UDF_match;

FUNCTION getMonth($date)
{
  match("[0-9]+-([0-9]+)-[0-9]+", $date)[1]
}

FUNCTION getMonths( $dates )
{
  FOR $date IN $dates
  RETURN getMonth($date)
}

FUNCTION getYear( $date )
{
	match("([0-9]+)-[0-9]+-[0-9]+", $date)[1]
}

<result>
   (
   FOR $m IN DISTINCT getMonths( document("items.xml")//item_tuple/end_date )
   LET $item := document("items.xml")//item_tuple[getYear(end_date) = 1999 AND getMonth(end_date) = $m]
   RETURN
      <monthly_result>
         <month> NUMFORMAT("##", $m) </month> ,
         <item_count> NUMFORMAT("###", count($item)) </item_count>
      </monthly_result> SORTBY (month)
   )
</result>