【解决】mysql 全连接问题

MySQL不支持全外连接，所以只能采取关键字UNION来联合左、右连接的方法

eg:

select *
from personinfo
LEFT JOIN sort
on personinfo.id = sort.id
UNION
select *
from personinfo
right JOIN sort
on personinfo.id = sort.id
where sort.id is not null