String Aggregation

Task:
Base Data:

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

Desired Output:

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



Now I know for sure you have come across this problem. This is usually super confusing for most newbies. Experts have their own ways of doing this.

ORACLE TO THE RESCUE!

Two new functions LISTAGG and wm_concat available in 11g release 2, help us solve this in a snap.

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

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

and

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

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

http://www.oracle-base.com/articles/misc/StringAggregationTechniques.php