oracle rank() over partition by queries

Does postgreSQL have an equivalent of the Oracle's "rank() over by
partition"?

Here's what i have so far but it doesn't work:

select id,
sum(case when key = 5 then 1 else 0 end),
sum(case when key = 6 then 1 when key = 7 then 1 else 0 end),
sum(case when l.status = 6 then cost when key = 7 then cost else
0 end),
RANK() OVER (ORDER BY sum(case when key = 6 then 1 when key = 7
then 1 else 0 end) DESC) AS RANK
from mytable
group by id