Oracle String Aggregation Techniques

This is a frequently asked question “How to display multiple rows in a single row as a delimited string”. It is basically string aggregation.

I will demonstrate the various techniques of string aggregation in Oracle SQL using the standard SCOTT.EMP table.

Oracle database 9i and up:

ROW_NUMBER() and SYS_CONNECT_BY_PATH

SQL> SELECT deptno,
  2         LTRIM(MAX(SYS_CONNECT_BY_PATH(ename,','))
  3            KEEP (DENSE_RANK LAST ORDER BY rn),',') AS emp_name
  4  FROM
  5    (SELECT deptno,
  6      ename,
  7      ROW_NUMBER() OVER (PARTITION BY deptno ORDER BY ename)    rn,
  8      ROW_NUMBER() OVER (PARTITION BY deptno ORDER BY ename) -1 rn_lag
  9    FROM emp
 10    )
 11  GROUP BY deptno
 12    CONNECT BY rn_lag = PRIOR rn
 13  AND deptno        = PRIOR deptno
 14    START WITH rn = 1
 15  ORDER BY deptno;

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

Oracle database 10g and up:

MODEL clause

SQL> select deptno
  2       , rtrim(ename,',') enames
  3  from ( select deptno
  4                , ename
  5                , rn
  6  from emp
  7  model
  8       partition by (deptno)
  9       dimension by (row_number() over
 10                    (partition by deptno order by ename) rn
 11                    )
 12       measures     (cast(ename as varchar2(40)) ename)
 13       rules
 14       ( ename[any] order by rn desc = ename[cv()]||','||ename[cv()+1]
 15         )
 16         )
 17   where rn = 1
 18   order by deptno
 19  /

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

Oracle database 11g Release 2 and up:

LISTAGG

SQL> SELECT deptno,
  2         LISTAGG(ename, ',') WITHIN GROUP (ORDER BY ename) AS emp_name
  3  FROM   emp
  4  GROUP BY deptno
  5  ORDER BY deptno;

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

Hope it helps!