Re: Outer join differences

Hi Tom,

Thanks for your prompt reply, after second thought(before receiving your
reply) I realized that postgres is doing more logically - i.e if the outer
join condition returns false then replace by nulls for right table columns.
We may change our code accordingly :-(.

Thanks
Yuva


-----Original Message-----
From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
Sent: Tuesday, July 30, 2002 9:15 PM
To: Yuva Chandolu
Cc: 'pgsql-hackers@postgresql.org'
Subject: Re: [HACKERS] Outer join differences 


Yuva Chandolu <ychandolu@ebates.com> writes:
> I see different results in Oracle and postgres for same outer join
queries.

I believe you are sending your bug report to the wrong database.

> When I run the query "select yt1_name, yt1_descr, yt2_name, yt2_descr from
> yuva_test1 left outer join yuva_test2 on yt1_id=yt2_id and yt2_name =
> '2-name2'" on postgres database I get the following results

> yt1_name    yt1_descr    yt2_name    yt2_descr
> 1-name1    1-descr1
> 1-name2    1-descr2    2-name2    2-descr2
> 1-name3    1-descr3
> 1-name4    1-descr4
> 1-name5    1-descr5
> 1-name6    1-descr6

> But when I tried the same on Oracle(8.1.7) (the query is "select yt1_name,
> yt1_descr, yt2_name, yt2_descr from yuva_test1, yuva_test2 where
> yt1_id=yt2_id(+) and yt2_name = '2-name2'') I get the following results

> yt1_name    yt1_descr    yt2_name    yt2_descr
> 1-name2    1-descr2    2-name2    2-descr2

According to the SQL spec, the output of a LEFT JOIN consists of those
joined rows where the join condition is true, plus those rows of the
left table for which no right-table row produced a true join condition
(substituting nulls for the right-table columns).  Our output clearly
conforms to the spec.

I do not know what Oracle thinks is the correct output when one
condition is marked with (+) and the other is not --- it's not very
obvious what that corresponds to in the spec's terminology.  But I
suggest you take it up with them, not us.
        regards, tom lane