postgresql json aggregate

Question

I\'m using postgres 9.4, I have the following query:

SELECT pid, code, name FROM activity, (
  SELECT code FROM project
) projects WHERE activity.pcode = project         


        

Answer 1

select
  pid,
  json_agg(json_build_object('code',code,'name',name))
from
  ...
group by
  pid

Answer 2

SELECT pid from activity a, (
    select json_agg(project) from project where code = a.code 
) as p

Something like that ...