On 09.03.26 21:21, Pierre Forstmann wrote:
Hello,
I can write a LISTAGG aggregate for:
create table emp(deptno numeric, ename text);
SELECT deptno, LISTAGG(ename, ','::text ORDER BY ename) AS employees
FROM emp GROUP BY deptno ORDER BY deptno;
I would like to know if is possible to create an aggregate LISTAGG that
would work like in Oracle:
SELECT deptno,
listagg(ename, ',') WITHIN GROUP (ORDER BY ename) AS employees
FROM emp
GROUP BY deptno
ORDER BY deptno;
I failed and IA also failed. Claude says:
It is not possible to exactly replicate listagg(ename, ',') WITHIN GROUP
(ORDER BY ename) as a custom PostgreSQL aggregate
because PostgreSQL strictly forbids ungrouped columns as direct
arguments to ordered-set aggregates.
Do you agree ?
One of the reasons that PostgreSQL hasn't implemented LISTAGG is that it
is a misdesign. It uses ordered-set aggregate syntax even
though it is not very similar to the other ordered-set aggregates.
Its syntax should be more similar to ARRAY_AGG or
JSON_ARRAYAGG, for example. But it's too late to fix the standard on this.
