Not able to use LISTAGG

Question

SELECT deptno, LISTAGG(ename, \',\') WITHIN GROUP (ORDER BY ename) AS employees
FROM   emp
GROUP BY deptno;

Answer 1

In this article you have different approaches to dealing with string aggegation, including those to take into account if you are running an Oracle version prior to 11g Release 2 (which is your scenario).

Particularly, you can use Oracle's WM_CONCAT function:

SELECT deptno, wm_concat(ename) AS employees
FROM   emp
GROUP BY deptno;

You can also define your own function for string aggregation or use other functions such as SYS_CONNECT_BY_PATH or COLLECT. In the above article you have examples of these methods.