IsNull(a.idNumber, b.IdNumber)
VFP中不能这样用吧

Create Cursor 表A (idNumber Char(10))
Insert Into 表A Values ('01')
Insert Into 表A Values ('02')
Insert Into 表A Values ('03')
Insert Into 表A Values ('04')
Insert Into 表A Values ('05')


Create Cursor 表B (idNumber Char(10))
Insert Into 表B Values ('02')
Insert Into 表B Values ('04')
Insert Into 表B Values ('06')
Insert Into 表B Values ('08')


Select Nvl(a.idNumber, b.IdNumber) ;
    From 表A a ;
    Full Join 表B b On a.idNumber = b.IdNumber ;
    Where IsNull(a.idNumber) Or IsNull(b.idNumber)

Create Cursor 表A (idNumber Char(10))
Insert Into 表A Values ('01')
Insert Into 表A Values ('02')
Insert Into 表A Values ('03')
Insert Into 表A Values ('04')
Insert Into 表A Values ('05')


Create Cursor 表B (idNumber Char(10))
Insert Into 表B Values ('02')
Insert Into 表B Values ('04')
Insert Into 表B Values ('06')
Insert Into 表B Values ('08')
SELECT * FROM 表A WHERE idNumber NOT in (SELECT * FROM 表B) ;
UNION SELECT * FROM 表B WHERE idNumber NOT in (SELECT * FROM 表A)