oracle sql listagg [duplicate]

Question

This question is an exact duplicate of:

• Not able to use LISTAGG 1 answer

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

Error:- ORA-00923: FROM keyword not found where expected 00923. 00000 - "FROM keyword not found where expected" *Cause:
*Action: Error at Line: 1 Column: 42

Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - 64bit Production

Answer 1

For the 10gR2 or 11gR1 versions of Oracle , you can use hierarchical queries with the contribution of sys_connect_by_path :

with emp( ename, deptno ) as
(
 select 'CLARK',10 from dual union all 
 select 'MILLER',10 from dual union all
 select 'KING',10 from dual union all
 select 'FORD',20 from dual union all
 select 'SCOTT',20 from dual union all
 select 'JONES',20 from dual union all
 select 'SMITH',20 from dual union all
 select 'ADAMS',20 from dual union all
 select 'WARD',30 from dual union all
 select 'MARTIN',30 from dual union all
 select 'TURNER',30 from dual union all
 select 'JAMES',30 from dual union all
 select 'ALLEN',30 from dual union all
 select 'BLAKE',30 from dual
)
select deptno, ltrim(sys_connect_by_path(ename, ','), ',') as enames
  from (select deptno,
               ename,
               row_number() over(partition by deptno order by ename) as rn
          from emp)
 where connect_by_isleaf = 1
connect by deptno = prior deptno
       and rn = prior rn + 1
 start with rn = 1;

DEPTNO  ENAMES
------  ------------------------------------
  10    CLARK,KING,MILLER
  20    ADAMS,FORD,JONES,SCOTT,SMITH
  30    ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD