Hi tom, when i tried use this wm_concat() function in 12c i'm getting this error can you briefly explain?

ORA-00904: “WM_CONCAT”: invalid identifier 00904. 00000 - “%s: invalid identifier and we said… WM_CONCAT is gone in 12c.

Use LISTAGG instead

SQL> SELECT deptno, listagg(ename, ',') WITHIN GROUP (ORDER BY ename) AS employees
  2  FROM   emp
  3  GROUP BY deptno;
 
    DEPTNO EMPLOYEES
---------- ------------------------------------------------------------
        10 CLARK,KING,MILLER
        20 ADAMS,FORD,JONES,SCOTT,SMITH
        30 ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD