Question

I have three basic queries that are related to each other and I need a single result set to return.

Simplified:

Query1 (possible return not a show stopper return null):

SELECT * FROM monkey WHERE monkey.ENDDATE IS NULL AND monkey.TEMPLATEID = 1

Query2 (possible return not a show stopper return null):

SELECT * FROM banana WHERE banana.ENDDATE IS NULL AND banana.TEMPLATEID = 1

Query3 (must return something):

SELECT * FROM tree WHERE tree.TEMPLATEID = 1

Query 1 and 2 may or may not return a value (come back null).

The third one will need to return a result (or not) IF the third query returns something I and query 1 or 2 fail I still want to return something.

I can’t do an outer join with 2 queries, because oracle won’t let me the error said… a.b (+) = b.b and a.c(+) = c.c is not allowed instead turn b+c into a view.

I think I understand the logical reason, never-the-less I need to return query 3 and maybe query 1, 2 or 1 and 2 along with 3 as a single result set.

I hope this makes sense.

Answer 1

You seem to be hitting ORA-01417. Using made up tables and data as you haven’t provided any, or the join conditions, I can get the same effect by trying to outer join monkey to both tree and banana – in a completely contrived way, of course:

with banana as (select 'yellow' as colour, 1 as template_id, null as enddate
        from dual),
    monkey as (select 'capuchin' as monkeytype, 1 as template_id, null as enddate
        from dual),
    tree as (select 'tropical' as treetype, 1 as template_id from dual)
select t.treetype, b.colour, m.monkeytype
from tree t, banana b, monkey m
where t.template_id = 1
and b.template_id (+) = t.template_id
and b.enddate (+) is null
and m.template_id (+) = t.template_id
and m.enddate (+) is null
and m.template_id (+) = b.template_id;

Error at Command Line:10 Column:22
Error report:
SQL Error: ORA-01417: a table may be outer joined to at most one other table
01417. 00000 -  "a table may be outer joined to at most one other table"
*Cause:    a.b (+) = b.b and a.c (+) = c.c is not allowed
*Action:   Check that this is really what you want, then join b and c first
           in a view.

if you use the ‘new’ (since 9i, I think) ANSI join syntax, rather the Oracle-specific (+) notation, you can do more:

with banana as (select 'yellow' as colour, 1 as template_id, null as enddate
        from dual),
    monkey as (select 'capuchin' as monkeytype, 1 as template_id, null as enddate
        from dual),
    tree as (select 'tropical' as treetype, 1 as template_id from dual)
select t.treetype, b.colour, m.monkeytype
from tree t
left join banana b on b.template_id = t.template_id
    and b.enddate is null
left join monkey m on m.template_id = t.template_id
    and m.enddate is null
    and m.template_id = b.template_id
where t.template_id = 1;

TREETYPE COLOUR MONKEYTYPE 
-------- ------ ---------- 
tropical yellow capuchin   

See the documentation for some of the restrictions on (+); Oracle recommend using the ANSI version, though they seem to use their own most of the time in examples in the documentation.