with affected_tasks as (
  select s.task_id
  from public.submissions s
  group by s.task_id
  having min(s.version_number) filter (where s.type <> 'amendment') = 1
     and count(*) filter (where s.type <> 'amendment' and s.version_number = 0) = 0
)
update public.submissions s
set version_number = s.version_number - 1
from affected_tasks a
where s.task_id = a.task_id;

with corrected_versions as (
  select
    s.task_id,
    coalesce(max(s.version_number) filter (where s.type <> 'amendment'), 0) as corrected_current_version
  from public.submissions s
  group by s.task_id
)
update public.tasks t
set current_version = cv.corrected_current_version
from corrected_versions cv
where t.id = cv.task_id
  and t.current_version is distinct from cv.corrected_current_version;