Db2 11.1

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select service_level from sysibmadm.env_inst_info;

SERVICE_LEVEL

DB2 v11.1.4.4

1 rows selected

-- 11.1 is the oldest Db2 here; LISTAGG, SQL/JSON and regular
-- expressions are all available
create table pet (owner varchar(10), name varchar(10));
insert into pet values ('ann','rex'),('ann','bo'),('bob','sam');

statement completed

select owner, listagg(name, ', ') within group (order by name) as pets
from pet group by owner order by owner;

OWNER
PETS

0 rows selected

select json_object('owner' value owner, 'pets' value count(*)) as doc
from pet group by owner order by owner;

DOC

0 rows selected