Left outer join functions like simple join

Question

I created two views SCO_REQGROSSLINES_V & SCO_REQLINESCOMPLETE on Oracle requisitions base tables. Our business rules enforce the following identity: the number of gross requisition lines will always be greater than or equal to the number of requisition lines complete. (By complete I mean delivered.)
Each view has a key named DATESUBINV_KEY constructed of a transaction date and the subinventory code using this logic:
, TO_CHAR(TRUNC(transaction_date),'YYYYMMDD') || subinventory_code
On 03-SEP-2010 a user created a requisition with one line item for material from the HEAT subinventory which was not delivered. This row is retuned in the result set when I query on SCO_REQGROSSLINES_V but is NOT returned when I query on SCO_REQLINESCOMPLETE. So far so good.
When I issue either of the the following left outer joins I do not get the row for the row for the HEAT subinventory on 03-SEP-2010:
select rgl.trxn_date
, rgl.subinventory
, rgl.line_count gross_line_count
, rgl.ext_prc gross_value
, rlc.line_count lines_filled
, rlc.ext_prc lines_filled_value
from SCO_REQGROSSLINES_V rgl left outer join sco_reqlinescomplete_v rlc
ON rgl.datesubinv_key = rlc.datesubinv_key
where rgl.TRXN_DATE BETWEEN to_date('29-AUG-2010') AND to_date('04-SEP-2010')
and rlc.trxn_date BETWEEN to_date('29-AUG-2010') AND to_date('04-SEP-2010')
order by rgl.trxn_date, rgl.subinventory
select rgl.trxn_date, rgl.subinventory
, rgl.line_count gross_line_count
, rgl.ext_prc gross_value
, rlc.line_count lines_filled
, rlc.ext_prc lines_filled_value
from SCO_REQGROSSLINES_V rgl
, sco_reqlinescomplete_v rlc
where rgl.TRXN_DATE BETWEEN to_date('29-AUG-2010') AND to_date('04-SEP-2010')
and rlc.trxn_date BETWEEN to_date('29-AUG-2010') AND to_date('04-SEP-2010')
AND rgl.datesubinv_key = rlc.datesubinv_key(+)
order by rgl.trxn_date, rgl.subinventory
Question: Why would the left outer joins function as a simple join on DATESUBINV_KEY? Do keys on views function differently than keys defined in the data dictionary? If they do how can I make these keys to function like data dictionary keys?

Answer 1

Hi,
The WHERE clause is applied after the outer join is completed. In your example, rows from rgl will be in the result set even if they have no match in rlc. In those cases, all the columns from rlc will be NULL.
Okay, so you have these rows that contain data from rgl but NULLs where the data from rlc was supposed to go. Now it's time to start the WHERE clause. You then apply conditions like this in the WHERE clause:
AND     rlc.trxn_date BETWEEN ...NULL is between anything, so the row that the outer join prodeuced is rejected.
All conditions involivn columns from rlc probably need to be part of the join condition, not the WHERE clause.
For example, in you first query the FROM and WHERE clauses might be:
FROM          sco_reqgrosslines_v      rgl
LEFT OUTER JOIN  sco_reqlinescomplete_v  rlc  ON    rgl.datesubinv_key   = rlc.datesubinv_key
                                        AND   rlc.trxn_date       BETWEEN TO_DATE ( '29-AUG-2010'
                                                                    , 'DD-MON-YYYY'
                                              AND       TO_DATE ( '04-SEP-2010'
                                                          , 'DD-MON-YYYY'
WHERE   rgl.trxn_date     BETWEEN TO_DATE ( '29-AUG-2010'
                         , 'DD-MON-YYYY'
               AND     TO_DATE ( '04-SEP-2010'
                         , 'DD-MON-YYYY'
                         )Always use (at least) two arguments when calling TO_DATE.
Conditions that only involve rgl can be in the WHERE clause, but if any conditions from rlc are in the WHERE clause, then the effect will be the same as an inner join.
There no difference between tables and views (or sub-queries) in this regard: the same thing would happen regardless of whether rgl and rlc were really tables or not.