Is there a way in Oracle to return multiple rows as a single string?

Question

Hi gurus,
I just got help from your guys fixing my dynamic sql problem. What I am doing in that function is to return a single string from multiple rows and I use it in the select statement. It works fine once the problem was solved. But is there any way in Oracle to do this in the select statement only? I have a table that stores incidents (incident_id is the PK) and another table that stores the people that are involved in an incident.
Incident_table
(incident_id number PK);
Incident_people_table
(incident_id number PK/FK,
person_id number PK);
Now in a report, I need to return the multiple rows of the Incident_People_table as a single string separated by a comma, for example, 'Ben, John, Mark'. I asked the SQL Server DBA about this and he told me he can do that in SQL Server by using a variable in the sql statement and SQL Server will auomatically iterate the rows and concatenate the result (I have not seen his actual work). Is there a similar way in Oracle? I have seen some examples here for some similar requests using the sys_connect_by_path, but I wonder if it is feasible in a report sql that is already rather complex. Or should I just stick to my simpler funcion?
Thanks.
Ben

Answer 1

Hi,
May be, this example will help you.
SQL> CREATE TABLE Incident_Table(
  2    incident_id number
  3  );
Table created.
SQL> CREATE TABLE Person_Table(
  2    person_id number,
  3    person_name VARCHAR2(200)
  4  );
Table created.
SQL> CREATE TABLE Incident_People_Table(
  2    incident_id number,
  3    person_id number
  4  );
Table created.
SQL> SELECT * FROM Incident_Table;
INCIDENT_ID
          1
          2
SQL> SELECT * FROM Person_Table;
PERSON_ID PERSON_NAME
         1 John
         2 Mark
         3 Ben
         4 Sam
SQL> SELECT * FROM Incident_People_Table;
INCIDENT_ID  PERSON_ID
          1          1
          1          2
          1          3
          2          1
          2          2
          2          4
6 rows selected.
SQL> SELECT IT.*,
  2    (
  3      WITH People_Order AS (
  4        SELECT IPT.incident_id, person_id, PT.person_name,
  5          ROW_NUMBER() OVER (PARTITION BY IPT.incident_id ORDER BY PT.person_name) AS Order_Num,
  6          COUNT(*) OVER (PARTITION BY IPT.incident_id) AS incident_people_cnt
  7        FROM Incident_People_Table IPT
  8          JOIN Person_Table PT USING(person_id)
  9      )
10      SELECT SUBSTR(SYS_CONNECT_BY_PATH(PO.person_name, ', '), 3) AS incident_people_list
11      FROM (SELECT * FROM People_Order PO WHERE PO.incident_id = IT.incident_id) PO
12      WHERE PO.incident_people_cnt = LEVEL
13      START WITH PO.Order_Num = 1
14      CONNECT BY PRIOR PO.Order_Num = PO.Order_Num - 1
15    ) AS incident_people_list
16  FROM Incident_Table IT
17  ;
INCIDENT_ID INCIDENT_PEOPLE_LIST
          1 Ben, John, Mark
          2 John, Mark, SamRegards,
Dima