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From: Pierre Forstmann <[email protected]>
To: [email protected] <[email protected]>
Subject: LISTAGG à la Oracle in PostgreSQL
Date: Mon, 9 Mar 2026 21:21:44 +0100
Message-ID: <[email protected]> (raw)

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 ?

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