Используйте SubQuery / CTE, оконную функцию SUM() OVER()
и STRING_AGG()
create table #t(org varchar(50), area int)
insert into #t values ('a',500),('b',200),('c',400);
select string_agg(org, ',') org, area
from
(
select org, sum(area) over() area
from #t
)t
group by area
или
select org, sum(area) area
from
(
select stuff(
(select ',' + org from #t for xml path('')), 1, 1, '') org, area
from #t tt
) t
group by org