没有任务的也要输出——>外联结left join
按照person的id升序排序——>order by ... asc
注意id是与person_id对应的，这俩才是联结条件。

select a.id,a.name,b.content 
from person a left join task b 
on a.id = b.person_id 
order by a.id asc;