弄了好久，结果发现--------　因为mysql没有full join这个东西 

你只能写成

sleect * from A left join B on A.id=B.id

union

select * from A.right join B on A.id=B.id

 

select person.FirstName,person.LastName,orders.OrderNo

from person

LEFT JOIN orders

ON person.id_p=orders.Id_p

UNION

select person.FirstName,person.LastName,orders.OrderNo

from person

RIGHT JOIN orders

ON person.id_p=orders.Id_p;