Re: BUG #3958: Self-Join Group-By Clause Produces Incorrect Results

Please disregard the previous email. After rereading what you sent, I realized that I need an outer join to A2 and not simply a self join...thanks and my apologies!

----- Original Message ----
From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: Marcus Torres <marcsf23(at)yahoo(dot)com>; pgsql-bugs(at)postgresql(dot)org
Sent: Wednesday, February 13, 2008 7:40:32 AM
Subject: Re: [BUGS] BUG #3958: Self-Join Group-By Clause Produces Incorrect Results

"Heikki
Linnakangas"
<heikki(at)enterprisedb(dot)com>
writes:
>
Marcus
Torres
wrote:
>>
I
wrote
a
simple
self-join
query
to
sum
the
transaction
count
of
different
>>
types
of
records
in
a
audit
table
and
the
result
set
for
the
different
sum
>>
totals
was
the
same
which
is
incorrect.

>
Looks
perfectly
correct
to
me.

Me
too.
The
underlying
data
before
grouping/aggregation
is

regression=#
select



A1.AUDIT_DATE,
P.CONTENT_POLICY_NAME,
A1.TXN_COUNT,
A2.TXN_COUNT
FROM
T_AUDIT
A1,



T_AUDIT
A2,



T_POLICY
P
WHERE
P.ID
=
A1.POLICY_ID

AND
P.ID
=
A2.POLICY_ID

AND
A1.POLICY_ID
=
A2.POLICY_ID

AND
A1.AUDIT_DATE
=
A2.AUDIT_DATE

AND
A1.AUDIT_TYPE_CODE
=
'CONTENT_1'

AND
A2.AUDIT_TYPE_CODE
=
'CONTENT_2';

audit_date
|
content_policy_name
|
txn_count
|
txn_count
------------+---------------------+-----------+-----------

2008-01-01
|
TEST
POLICY




|




1
|




1

2008-01-01
|
TEST
POLICY




|




1
|




1

2008-01-01
|
TEST
POLICY




|




1
|




1

2008-01-01
|
TEST
POLICY




|




1
|




1

2008-01-01
|
TEST
POLICY




|




1
|




1

2008-01-01
|
TEST
POLICY




|




1
|




1

2008-01-01
|
TEST
POLICY




|




1
|




1

2008-01-01
|
TEST
POLICY




|




1
|




1

2008-01-01
|
TEST
POLICY




|




1
|




1

2008-01-01
|
TEST
POLICY




|




1
|




1
(10
rows)

from
which
it's
clear
that
given
all
ones
in
txn_count,
the
sums
*must*
be
the
same
because
they're
taken
over
the
same
number
of
rows.

I
suspect
what
the
OP
needs
is
two
separate
queries
(perhaps
union'ed
together)
not
a
self-join.

regards,
tom
lane

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