Left Outer Join

Database
Enthusiast

Left Outer Join

I have a basic question on joins
I have 2 tables employee(upi--empno) and department(upi---deptno)

i AM RUNNING FOLLOWING QUERY
sel e.empno,e.deptno,e.name
from employee e left outer join department d
on e.deptno=d.deptno
and e.empno=d.mgrno
where d.deptno is null;

With a Explain as below:
4) We do an all-AMPs RETRIEVE step from PRAKHAR1.e by way of an
all-rows scan with no residual conditions into Spool 2 (all_amps),
which is redistributed by hash code to all AMPs. Then we do a
SORT to order Spool 2 by row hash. The size of Spool 2 is
estimated with low confidence to be 26 rows. The estimated time
for this step is 0.01 seconds.
5) We do an all-AMPs JOIN step from Spool 2 (Last Use) by way of a
RowHash match scan, which is joined to PRAKHAR1.d by way of a
RowHash match scan with no residual conditions. Spool 2 and
PRAKHAR1.d are left outer joined using a merge join, with a join
condition of ("(EmpNo = PRAKHAR1.d.MgrNo) AND (DeptNo =
PRAKHAR1.d.DeptNo)"). The result goes into Spool 3 (all_amps),
which is built locally on the AMPs. The size of Spool 3 is
estimated with low confidence to be 26 rows. The estimated time
for this step is 0.01 seconds.
6) We do an all-AMPs RETRIEVE step from Spool 3 (Last Use) by way of
an all-rows scan with a condition of ("DeptNo IS NULL") into Spool
1 (group_amps), which is built locally on the AMPs. The size of
Spool 1 is estimated with low confidence to be 26 rows. The
estimated time for this step is 0.04 seconds.

Although Department table is joined on two values 1 UPI other non index(mgrno)...why this table was not redistributed by generating hash on (deptno,mgrno)?
does that mean redistribution done on 4th step was on deptno only?
Please provide some valid input as i might be misinterpreting ?