I am not too familiar with the ACCESS but I believe this has something to do with outer joins. You can use the following as example:
EMP table
EMP_NO DEPTNO
--------------- ---------------
1 10
2 20
3 30
DEPT table
DEPTNO DEPTNAME
--------------- ----------
10 TOKYO
20 NEW YORK
the LEFT join:
SELECT b.emp_no, b.deptno, a.deptno
FROM dept a, emp b
WHERE a.deptno(+) = b.deptno;
the RIGHT join:
SELECT a.emp_no, a.deptno, b.deptno
FROM emp a, dept b
WHERE a.deptno = b.deptno(+);
EMP_NO DEPTNO DEPTNO
--------------- --------------- ---------------
1 10 10
2 20 20
3 30
Its just a matter of positioning of the driving table and the need for the SQl to use such join.
Hope my info helps.