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Re: Outer join differences

From: Yuva Chandolu <ychandolu(at)ebates(dot)com>
To: 'Tom Lane' <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "'pgsql-hackers(at)postgresql(dot)org'" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Outer join differences
Date: 2002-07-31 04:29:48
Message-ID: A0F24737FCB34F489EC955D143BDD8510173E0F1@exchange-sf1.corp.ebates.com (view raw or flat)
Thread:
Lists: pgsql-hackers
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(at)sss(dot)pgh(dot)pa(dot)us]
Sent: Tuesday, July 30, 2002 9:15 PM
To: Yuva Chandolu
Cc: 'pgsql-hackers(at)postgresql(dot)org'
Subject: Re: [HACKERS] Outer join differences 


Yuva Chandolu <ychandolu(at)ebates(dot)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

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Subject: Re: Why is MySQL more chosen over PostgreSQL?
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