1,
select a.field1,a.field2,a.field3,a.field4,a.field5,b.field6,b.field7
from a full outer join b
on a.field3=b.field3 and a.field4=b.field4 and a.field5=b.field5
2,
select a.field1,a.field2,a.field3,a.field4,a.field5,'' field6, '' field7
from a
union all
select '' field1,'' field2,b.field3,b.field4,b.field5,b.field6,b.field7
from b