select date_enter, string_agg(login,',') as login_LIST from(
select date_enter ,login
from
(values ('1','Vasy','01-01-2021'),('2','Vasy','02-01-2021'::date),('3','Vasy','03-01-2021'::date),('4','Oly','02-01-2021'::date),('5','Oly','03-01-2021'::date),('6','Oly','03-01-2021'::date) ) as T (uud,login, date_enter )
group by date_enter::date ,login) tt
group by date_enter::date
без претензии на оптимизацию