gistfile1.txt

create table task(
  id int primary key,
  status varchar(10)
);

create table subtask(
  id int primary key,
  task_id int references task(id),
  status varchar(10)
);

insert into task values (1, 'ready');
insert into subtask values (1, 1, 'ready');
insert into subtask values (2, 1, 'ready');
insert into subtask values (3, 1, 'processing');
-- when all subtasks are ready, I want task to be ready