Why is Discoverer adding outer joins?

Question

Hi,
I have set up standard joins (i.e. no outer joins) between one master and two detail folders in the Admin. For some reason when I create a report using the three folders, Discoverer is making them outer joins. Note: This query will cause a fan trap but there is a business reason for doing so (disable fan trap detection is checked). I'm using Plus/Web for the report.
Why is Discoverer adding outer joins?
Thanks, Andrew
This is what I expect (note one master joined to two details):
SELECT
O125508.BUSINESS_TRANSACTION_CODE,
O141221.SOURCE,
O141221.AMOUNT
FROM IRIS.IRS_ACQUIRED_INFO_V O125508,
IRIS.IRS_FUNDINGS_V O141221,
IRIS.IRS_FUNDING_SELECTIONS_V O144361
WHERE ( ( O125508.BUSINESS_TRANSACTION_ID = O141221.BUSINESS_TRANSACTION_ID )
AND ( O125508.BUSINESS_TRANSACTION_ID = O144361.BUSINESS_TRANSACTION_ID )
AND ( O144361.SOURCE = :"Source" )
AND ( O125508.BUSINESS_TRANSACTION_CODE = :"Business Transaction Code" )
This is what Discoverer is generating (note duplicate masters {IRS_ACQUIRED_INFO_V} with outer joins):
SELECT
O125509.BUSINESS_TRANSACTION_CODE,
O141221.SOURCE,
O141221.AMOUNT
FROM IRIS.IRS_ACQUIRED_INFO_V O125508,
IRIS.IRS_FUNDINGS_V O141221,
IRIS.IRS_ACQUIRED_INFO_V O125509,
IRIS.IRS_FUNDING_SELECTIONS_V O144361
WHERE ( ( O125509.BUSINESS_TRANSACTION_ID = O125508.BUSINESS_TRANSACTION_ID ) )
AND ( O125508.BUSINESS_TRANSACTION_ID = O141221.BUSINESS_TRANSACTION_ID(+) )
AND ( O125509.BUSINESS_TRANSACTION_ID = O144361.BUSINESS_TRANSACTION_ID(+) )
AND ( O144361.SOURCE(+) = :"Source" )
AND ( O125509.BUSINESS_TRANSACTION_CODE = :"Business Transaction Code" )
Edited by: cfandrew on Mar 26, 2009 12:36 PM

Answer 1

Rod,
You’re correct in that the “source” field in the query (aka: select portion) is different than the “source” field in the condition - but this is on purpose.
Here is a good analogy. Department has many Employees. The business question is to give me all employees in Andy’s Dept (but you don't know what department Andy is in, so you have to have the query reverse engineer Andy's department and then go back and get all the employees in that department).
The raw query/data without the condition causes a fan trap and looks like this:
select d.dept_name, e1.emp_name, e2.emp_name
from dept d
,emp e1
,emp e2
where d.dept_id = e1.dept_id
and d.dept_id = e2.dept_id
Dept Name....Emp Name 1....Emp_Name 2
Services.....Joe....................Joe
Services.....Joe....................Jane
Services.....Jane..................Joe
Services.....Jane..................Jane
IT.............Andy.................Andy
IT.............Andy.................Sara
IT.............Sara..................Andy
IT.............Sara..................Sara          
Billing.........Bill.....................Bill
And this is what we want:
select d.dept_name, e2.emp_name
from dept d
,emp e1
,emp e2
where d.dept_id = e1. dept_id
and d.dept_id = e2. dept_id
and e1.emp_name = 'Andy'
Dept Name...Emp_Name 2
IT...............Andy
IT...............Sara
And this is what Discoverer is providing:
select d2.dept_name, e2.emp_name
from dept d1
,dept d2
,emp e1
,emp e2
where d2.dept_id = d1.dept_id
and d1.dept_id = e1.dept_id(+)
and d2.dept_id = e2.dept_id(+)
and e1.emp_name(+) = 'Andy'
Dept Name....Emp_Name 2
Service..........Joe
Service..........Jane
IT.................Andy
IT.................Sara
Billing.............Bill
Also, DisableAutoOuterJoinsOnFilters is set to 1.
Thanks for your help!
Andy