How to pass parameter into extract function (for XMLTYPE)

Question

I have a table PROBLEMXML with XMLTYPE field xml_column. In this column there are several deffinitions for the problem. There is no max amount of deffinitions and it can be no definition at all. I need to return all definitions for every problem as a string wirh definitions separated by ";".
Query
SELECT extract(prob.Def,'/Definitions/Definition[1]/@var') || ';'|| extract(prob.Def,'/Definitions/Definition[2]/@var')
FROM PROBLEMXML j ,
XMLTABLE (
'/problem'
PASSING j.xml_column
COLUMNS probid VARCHAR (31) PATH '/problem/@id',
Def XMLTYPE PATH '/problem/Definitions') prob
where PROBLEM_ID =1;
returns exactly what I want a;m.
But
declare
my_var varchar2(2000) :=null;
n1 number;
n2 number;
begin
n1:=1;
n2:=2;
SELECT extract(prob.Def,'/Definitions/Definition[n1]/@var') || '|'|| extract(prob.Def,'/Definitions/Definition[n2]/@var') into my_var
FROM ETL_PROBLEMXML_STG_T j ,
XMLTABLE (
'/problem'
PASSING j.xml_column
COLUMNS probid VARCHAR (31) PATH '/problem/@id',
Def XMLTYPE PATH '/problem/Definitions') prob
where PROBLEM_ID =1;
dbms_output.put_line(my_var);
end;
returns NULL.
Is there is a way to pass parameter into extract function?

Answer 1

I need to return all definitions for every problem as a string wirh definitions separated by ";".In XQuery, there's the handy function "string-join" for that.
For example :
SQL> WITH etl_problemxml_stg_t AS (
  2   SELECT 1 problem_id,
  3  xmltype('<problem id="1">
  4   <Definitions>
  5    <Definition var="var1"></Definition>
  6    <Definition var="var2"></Definition>
  7    <Definition var="var3"></Definition>
  8   </Definitions>
  9  </problem>') xml_column
10   FROM dual
11  )
12  SELECT j.problem_id,
13         prob.probid,
14         prob.def
15  FROM etl_problemxml_stg_t j,
16       XMLTable(
17        'for $i in /problem
18         return element r
19         {
20          $i/@id,
21          element d { string-join($i/Definitions/Definition/@var, ";") }
22         }'
23        passing j.xml_column
24        columns
25         probid varchar2(30)  path '@id',
26         def    varchar2(100) path 'd'
27       ) prob
28  ;
PROBLEM_ID PROBID               DEF
         1 1                    var1;var2;var3