Outer join that give no result

Question

Hi everybody
Here are the scripts
CREATE TABLE dem_comment (
COMMENTID VARCHAR2(50 BYTE) NOT NULL,
PARENTID VARCHAR2(50 BYTE) NOT NULL,
DEM_DATE_CREATION_MEMO date)
CREATE TABLE demand(
NUM_PCE VARCHAR2(14 BYTE) NOT NULL,
NUM_DEMANDE VARCHAR2(8 BYTE)
insert into dem_comment VALUES (1,'12345ABCDEF',to_date('17/08/2012 10:18:34','DD/mm/YYyy HH:MI:SS'))
insert into demand values('12345','ABCDEF')
And the following is the request that have the problem
select dem.NUM_PCE, memo.parentid
from demand dem, dem_comment memo
where CONCAT(dem.NUM_PCE,dem.NUM_DEMANDE) = memo.parentId (+)
and memo.DEM_DATE_CREATION_MEMO = (select MAX(DEM_DATE_CREATION_MEMO)
FROM dem_comment memo
WHERE memo.parentId = CONCAT(dem.NUM_PCE,dem.NUM_DEMANDE))
And the result is the one i m waiting for
NUMPCE | PARENTID
12345 | 12345ABCDEF
but when i delete the record from dem_comment, (because of the outer join) i m supposed to have something like
NUMPCE | PARENTID
12345 |
but the result is that, no record
NUMPCE | PARENTID
The outer join seems to not work
Thank you for your help

Answer 1

UW (Germany) wrote:
Sorry, I was too fast and did not notice the nested select. Try this:
select dem.NUM_PCE, memo.parentid
from demand dem
left outer join dem_comment memo on CONCAT(dem.NUM_PCE,dem.NUM_DEMANDE) = memo.parentId
where memo.DEM_DATE_CREATION_MEMO is null
or memo.DEM_DATE_CREATION_MEMO = (select MAX(DEM_DATE_CREATION_MEMO)
FROM dem_comment memo
WHERE memo.parentId = CONCAT(dem.NUM_PCE,dem.NUM_DEMANDE));
It is an left outer join, so the predicate on the left table belongs in the on clause
from demand dem
left outer join dem_comment memo
on CONCAT(dem.NUM_PCE,dem.NUM_DEMANDE) = memo.parentId
and
memo.DEM_DATE_CREATION_MEMO = (select MAX(DEM_DATE_CREATION_MEMO)
                                        FROM dem_comment memo
                                      WHERE memo.parentId = CONCAT(dem.NUM_PCE,dem.NUM_DEMANDE))