I'm trying to write a select statement that will join one portfolio of items
with another, and retain the items that neither portfolio has in common. For
example, if I have Portfolio 'A' with

ID Value
1 A
2 B
3 C

And portfolio 'B' with

1 A
3 C
4 D

I'd like to get a result set like this

1 A 1 A
2 B null null
3 C 3 C
null null 4 D

I'm using a self join on a table beginning with a left outer join, then a
union with the same query using a right outer join, but it doesn't seem to
work.Any suggestions, please! I'm lost and facing a deadline. Other
approaches welcome. I'm trying to this is a stored procedure and I need to
calculate the differences between the portfolios. Actual code that doesn't
work is below:

select
h0.sec_id,
h0.HLDG_SHARES,
h0.HLDG_MKT_VALUE,
h0.HLDG_PAR_VALUE,
h.sec_id,
h.HLDG_SHARES,
h.HLDG_MKT_VALUE,
h.HLDG_PAR_VALUE,
h.HLDG_SEQNO
from holdings h0 left outer join
holdings h on h0.sec_id=h.sec_id
where h0.hsd_doc_id=40022 and
h.hsd_doc_id=42519
and h0.hldg_seqno >0
union
select
h0.sec_id,
h0.HLDG_SHARES,
h0.HLDG_MKT_VALUE,
h0.HLDG_PAR_VALUE,
h.sec_id,
h.HLDG_SHARES,
h.HLDG_MKT_VALUE,
h.HLDG_PAR_VALUE,
h.HLDG_SEQNO
from holdings h0 right outer join
holdings h on h0.sec_id=h.sec_id
where h0.hsd_doc_id=40022 and
h.hsd_doc_id=42519
and h0.hldg_seqno >0
order by 1,5