select * from road as A join project as B on A.planId=B.projectId and B.projectcode is not null
或
select * from road whre planId in
(select projectId from project whre B.projectcode is not nlull )
或
select * from road whre planId in
(select projectId from project whre B.projectcode is not nlull )
呵呵
请自行验证