comma-separated list as a result of select statement in Oracle [duplicate]

Question

This question already has an answer here:

• How can I combine multiple rows into a comma-delimited list in Oracle? [duplicate] 11 answers

I have a table named "person". It contains person's id and it's parent id (only one parent is possible). As a result of a query, I want a table with first column - a person id, and a second column - a list of it's children id's. How exactly to do this? I've read about listagg function, but I'm not sure if it is appropriate for my purpose. And this query produces an empty second column:

select t1.id, (select t2.id from person t2 where t2.parent_id = t1.id) from person t1 where t1.status = 'parent';

Answer 1

SELECT parent_id,
       RTRIM(XMLAGG(XMLELEMENT(e,child_id || ',')).EXTRACT('//text()'),',') AS "Children"
  FROM parentChildTable
 WHERE parent_id = 0
 GROUP BY parent_id

or

SELECT parent_id,
       LISTAGG(child_id, ',') WITHIN GROUP (ORDER BY child_id) AS "Children"
  FROM parentChildTable
 WHERE parent_id = 0
 GROUP BY parent_id

Answer 2

Mark's implementation of LISTAGG is definitely the way to go for ORacle 11GR2. For For 11GR1 or Oracle 10 you can use wmsys.wm_Concat instead in exactly the same way (may require a permissions grant from your DBA)

Answer 3

Just another way to approach it ...

SELECT parent_id,max(child_list) FROM (
  SELECT parent_id,sys_connect_by_path(child_number,',') child_list FROM (
    SELECT parent_id, id,
           row_number() over (partition by parent_id order by id) child_number
      FROM person
      WHERE parent_id IS NOT NULL
  )
  START WITH child_number=1
  CONNECT BY parent_id = PRIOR parent_id AND child_number = PRIOR child_number + 1
)
GROUP BY parent_id
ORDER BY parent_id
;

Answer 4

SELECT wmsys.wm_concat() FROM ;

It's controversial, but it works - https://forums.oracle.com/forums/thread.jspa?threadID=2205545