Have a read of the following link. I consider this quite helpful information.
SAS(R) 9.2 SQL Procedure User's Guide
As a variation of "Producing Rows from the First Query or the Second Query" below code should do:
proc sql;
create table want as
select * from Company
where Deptid not in (select Deptid from Dept)
outer union corr
select * from Dept
where Deptid not in (select Deptid from Company)
;
quit;