模板：

FOR var IN REVERSE 1..10 LOOP
    statement_list
END LOOP;

举例：

create or replace function insert_user_roles()
returns void as $$
declare
  user RECORD;
  role RECORD;
begin
  for user in (select id from user where is_delete = false) loop
    for role in (select * from role where is_delete = false) loop
      insert into '实际要插入数据的表' ('字段')
      values
      (user.id, role.id);
    end loop;
  end loop;
end;
$$ language plpgsql;
 
select insert_user_roles();;