Invalid combinations of joins involving outer joins

Question

Hi all, I have the following problem
Scenario: I created 6 custom folders:
Tasks (with measures)
Type
Criticity
Status
Owners
Assignees
The first folder is used to retrieve how many tasks (COUNT(tasks)) have a particular type or status or a combination between them, and the others 5 are dimensions.
I create 6 joins starting always from the dimensions in this way (radio buttons):
Detail item values always exist in master folder (Typical)
Outer join on detail
where the master is always a dimension and the detail is always the custom folder with the measures.
I put the outer join on the custom folder with the measures because I want to show '0' in case I don't have any record on this folder for a specific attribute on a dimension (the join fails).
I saw that if I put the outer join on the master (dimensions), when the join fails I don't see at all the information regarding that particular dimension.
For example
I select 2 folder: Tasks and Assignee
join: Tasks.task_id (+) = Assignee.task_id
Result:
TASK ASSIGNEE
10 Mr. A
20 Mr. B
30 Mr. C
0 Mr. D
Just to make a test, If I change the join on Administrator putting :
Detail item values might not exist in master folder
Outer join on master
...the result is this
TASK ASSIGNEE
10 Mr. A
20 Mr. B
30 Mr. C
...I don't see the last record.
The customer asked to see always the record with task =0 (if exists), so I joined all the custom folders as I expalned above, but when I try to link (on Discoverer Plus) more than two tasks I have the following error:
Invalid combinations of joins involving outer joins
So, my question is this: how can I avoid this error ? Does it exist any trick or another way to link the custom folders (showing always the records with '0' when the join doesn't retrieve nothing ) ?
Thanks in advance
Alex

Answer 1

Well I will take a stab at answering this. The problem is not knowing what is in your custom folders. Also not knowing the specifics on your Discoverer Join definitions. On something like this you may be better going to Oracle support, since they can start a Web Conference and see exactly what you see, and can check out the various possibilities. All we here can do is make guesses, and the guesses could be wrong.
You do have to be careful in your join definitions in Discoverer. You have to pick the correct table as the Master table, and the correct table as the Detail table. Mess that up and you can mess yourself up. So my first though is check your join definition. Sounds like you want assigned to be the master table. Then tasks would be the detail table.
Then you want to pick the option that detail items might not exist in master. Which it looks like you have done.
Then for the other options, Oracle, in my mind, does the opposite of what I would think to pick. If you pick OUTER JOIN ON DETAIL, that will include the Master items with no detail items. So that is what you need to pick.
Looks like you did the OUTER JOIN ON MASTER, which means will include detail items with no master. Since you had a master with no detail, it will not show, and that is why the Mr. D does not show.
I always have to do the help on this because it is opposite of what I would expect - my mind thinks outer join on master should include all masters. Nope, it has to be the outer join on detail to do that.
The master with no detail will probably show a NULL value in the column for the detail, instead of 0. You could convert the null value to display as a 0.
Hope this helps a bit. Just remember that I am guessing/speculating on a possible cause.
John Dickey