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484 lines
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From owner-pgsql-sql@hub.org Sat Jul 10 16:31:14 1999
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Sat, 10 Jul 1999 16:16:42 -0400 (EDT)
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(envelope-from oleg@sai.msu.su)
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Sun, 11 Jul 1999 00:16:40 +0400 (MSD)
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Date: Sun, 11 Jul 1999 00:16:39 +0400 (MSD)
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From: Oleg Bartunov <oleg@sai.msu.su>
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X-Sender: megera@ra
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Reply-To: Oleg Bartunov <oleg@sai.msu.su>
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To: hackers@postgreSQL.org
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cc: pgsql-sql@postgreSQL.org
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Subject: [SQL] SELECT DISTINCT question
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Message-ID: <Pine.GSO.3.96.SK.990711000908.2043R-100000@ra>
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Organization: Sternberg Astronomical Institute (Moscow University)
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MIME-Version: 1.0
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Content-Type: TEXT/PLAIN; charset=US-ASCII
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Sender: owner-pgsql-sql@postgreSQL.org
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Precedence: bulk
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Status: RO
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I got a problem with query:
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select distinct (date), bytes from access_log;
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which works but not as I expect. I thought this query will select
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all rows with distinct values of 'date' column, but it get
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distinct pairs 'date, bytes' . From documnetation I see
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"DISTINCT will eliminate all duplicate rows from the selection.
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DISTINCT ON column will eliminate all duplicates in the specified column;
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this is equivalent to using GROUP BY column.
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ALL will return all candidate rows, including duplicates."
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discovery=> select distinct on date,bytes from access_log;
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ERROR: parser: parse error at or near ","
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Regards,
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Oleg
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_____________________________________________________________
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Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
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Sternberg Astronomical Institute, Moscow University (Russia)
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Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
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phone: +007(095)939-16-83, +007(095)939-23-83
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From owner-pgsql-sql@hub.org Sat Jul 10 18:01:17 1999
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Sat, 10 Jul 1999 17:18:28 -0400 (EDT)
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To: Oleg Bartunov <oleg@sai.msu.su>
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cc: hackers@postgreSQL.org, pgsql-sql@postgreSQL.org
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Subject: [SQL] Re: [HACKERS] SELECT DISTINCT question
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In-reply-to: Your message of Sun, 11 Jul 1999 00:16:39 +0400 (MSD)
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<Pine.GSO.3.96.SK.990711000908.2043R-100000@ra>
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Date: Sat, 10 Jul 1999 17:18:28 -0400
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Message-ID: <5707.931641508@sss.pgh.pa.us>
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Sender: owner-pgsql-sql@postgreSQL.org
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Precedence: bulk
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Status: RO
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Oleg Bartunov <oleg@sai.msu.su> writes:
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> discovery=> select distinct on date,bytes from access_log;
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> ERROR: parser: parse error at or near ","
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The syntax for SELECT DISTINCT ON is just as brain-damaged as the
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functionality itself: there's no comma after the column name.
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You want
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select distinct on date date,bytes from access_log;
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The reason the functionality is brain-damaged is that there's no way to
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know which tuple out of the set of tuples with a given "date" value will
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be the one returned.
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SELECT DISTINCT ON is not in SQL92, and I think it shouldn't be in
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Postgres either...
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regards, tom lane
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From owner-pgsql-sql@hub.org Sun Jul 11 12:01:23 1999
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for <maillist@candle.pha.pa.us>; Sun, 11 Jul 1999 12:01:22 -0400 (EDT)
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Sun, 11 Jul 1999 11:41:38 -0400 (EDT)
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(envelope-from oleg@sai.msu.su)
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Sun, 11 Jul 1999 10:09:24 +0400 (MSD)
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Date: Sun, 11 Jul 1999 10:09:24 +0400 (MSD)
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From: Oleg Bartunov <oleg@sai.msu.su>
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X-Sender: megera@ra
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To: Tom Lane <tgl@sss.pgh.pa.us>
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cc: hackers@postgreSQL.org, pgsql-sql@postgreSQL.org
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Subject: Re: [SQL] Re: [HACKERS] SELECT DISTINCT question
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In-Reply-To: <5707.931641508@sss.pgh.pa.us>
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Message-ID: <Pine.GSO.3.96.SK.990711100405.2043V-100000@ra>
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Organization: Sternberg Astronomical Institute (Moscow University)
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MIME-Version: 1.0
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Content-Type: TEXT/PLAIN; charset=US-ASCII
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Sender: owner-pgsql-sql@postgreSQL.org
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Precedence: bulk
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Status: RO
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On Sat, 10 Jul 1999, Tom Lane wrote:
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> Date: Sat, 10 Jul 1999 17:18:28 -0400
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> From: Tom Lane <tgl@sss.pgh.pa.us>
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> To: Oleg Bartunov <oleg@sai.msu.su>
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> Cc: hackers@postgreSQL.org, pgsql-sql@postgreSQL.org
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> Subject: [SQL] Re: [HACKERS] SELECT DISTINCT question
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>
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> Oleg Bartunov <oleg@sai.msu.su> writes:
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> > discovery=> select distinct on date,bytes from access_log;
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> > ERROR: parser: parse error at or near ","
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>
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> The syntax for SELECT DISTINCT ON is just as brain-damaged as the
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> functionality itself: there's no comma after the column name.
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> You want
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>
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> select distinct on date date,bytes from access_log;
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>
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thanks, this works. But why parser complains about such query:
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discovery=> select distinct on a.date a.date, a.bytes from access_log a;
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ERROR: parser: parse error at or near "."
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In this query I could just omit '.', but in more complex query
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I probably could need one.
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> The reason the functionality is brain-damaged is that there's no way to
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> know which tuple out of the set of tuples with a given "date" value will
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> be the one returned.
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>
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> SELECT DISTINCT ON is not in SQL92, and I think it shouldn't be in
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> Postgres either...
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|
|
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I'm not an SQL expert, but if it works and this feature is in standard
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but only syntax is diffrent, why just not to use standard
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select distinct(date), bytes from access_log;
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Or I'm missing here ?
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Regards,
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Oleg
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>
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> regards, tom lane
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>
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_____________________________________________________________
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Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
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|
Sternberg Astronomical Institute, Moscow University (Russia)
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Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
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phone: +007(095)939-16-83, +007(095)939-23-83
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From owner-pgsql-hackers@hub.org Sun Jul 11 12:01:26 1999
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Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
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Received: from hub.org (hub.org [209.167.229.1]) by renoir.op.net (o1/$ Revision: 1.18 $) with ESMTP id LAA15017 for <maillist@candle.pha.pa.us>; Sun, 11 Jul 1999 11:59:07 -0400 (EDT)
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Sun, 11 Jul 1999 11:41:38 -0400 (EDT)
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(envelope-from oleg@sai.msu.su)
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Sun, 11 Jul 1999 10:09:24 +0400 (MSD)
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Date: Sun, 11 Jul 1999 10:09:24 +0400 (MSD)
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From: Oleg Bartunov <oleg@sai.msu.su>
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X-Sender: megera@ra
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To: Tom Lane <tgl@sss.pgh.pa.us>
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cc: hackers@postgreSQL.org, pgsql-sql@postgreSQL.org
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Subject: Re: [SQL] Re: [HACKERS] SELECT DISTINCT question
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In-Reply-To: <5707.931641508@sss.pgh.pa.us>
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Message-ID: <Pine.GSO.3.96.SK.990711100405.2043V-100000@ra>
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Organization: Sternberg Astronomical Institute (Moscow University)
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MIME-Version: 1.0
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Content-Type: TEXT/PLAIN; charset=US-ASCII
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: RO
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On Sat, 10 Jul 1999, Tom Lane wrote:
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> Date: Sat, 10 Jul 1999 17:18:28 -0400
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> From: Tom Lane <tgl@sss.pgh.pa.us>
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> To: Oleg Bartunov <oleg@sai.msu.su>
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> Cc: hackers@postgreSQL.org, pgsql-sql@postgreSQL.org
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> Subject: [SQL] Re: [HACKERS] SELECT DISTINCT question
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>
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> Oleg Bartunov <oleg@sai.msu.su> writes:
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> > discovery=> select distinct on date,bytes from access_log;
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> > ERROR: parser: parse error at or near ","
|
|
>
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|
> The syntax for SELECT DISTINCT ON is just as brain-damaged as the
|
|
> functionality itself: there's no comma after the column name.
|
|
> You want
|
|
>
|
|
> select distinct on date date,bytes from access_log;
|
|
>
|
|
|
|
thanks, this works. But why parser complains about such query:
|
|
|
|
discovery=> select distinct on a.date a.date, a.bytes from access_log a;
|
|
ERROR: parser: parse error at or near "."
|
|
|
|
In this query I could just omit '.', but in more complex query
|
|
I probably could need one.
|
|
|
|
> The reason the functionality is brain-damaged is that there's no way to
|
|
> know which tuple out of the set of tuples with a given "date" value will
|
|
> be the one returned.
|
|
>
|
|
> SELECT DISTINCT ON is not in SQL92, and I think it shouldn't be in
|
|
> Postgres either...
|
|
|
|
|
|
I'm not an SQL expert, but if it works and this feature is in standard
|
|
but only syntax is diffrent, why just not to use standard
|
|
|
|
select distinct(date), bytes from access_log;
|
|
|
|
Or I'm missing here ?
|
|
|
|
|
|
Regards,
|
|
Oleg
|
|
>
|
|
> regards, tom lane
|
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>
|
|
|
|
_____________________________________________________________
|
|
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
|
|
Sternberg Astronomical Institute, Moscow University (Russia)
|
|
Internet: oleg@sai.msu.su, http://www.sai.msu.su/~megera/
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|
phone: +007(095)939-16-83, +007(095)939-23-83
|
|
|
|
|
|
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|
From owner-pgsql-sql@hub.org Sun Jul 11 12:01:16 1999
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|
Received: from renoir.op.net (root@renoir.op.net [209.152.193.4])
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for <maillist@candle.pha.pa.us>; Sun, 11 Jul 1999 12:01:15 -0400 (EDT)
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(envelope-from owner-pgsql-sql@hub.org)
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Sun, 11 Jul 1999 11:38:44 -0400 (EDT)
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To: Oleg Bartunov <oleg@sai.msu.su>
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cc: hackers@postgreSQL.org, pgsql-sql@postgreSQL.org
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Subject: Re: [SQL] Re: [HACKERS] SELECT DISTINCT question
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In-reply-to: Your message of Sun, 11 Jul 1999 10:09:24 +0400 (MSD)
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<Pine.GSO.3.96.SK.990711100405.2043V-100000@ra>
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Date: Sun, 11 Jul 1999 11:38:43 -0400
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Message-ID: <15129.931707523@sss.pgh.pa.us>
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Sender: owner-pgsql-sql@postgreSQL.org
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Precedence: bulk
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Status: RO
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Oleg Bartunov <oleg@sai.msu.su> writes:
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> thanks, this works. But why parser complains about such query:
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> discovery=> select distinct on a.date a.date, a.bytes from access_log a;
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> ERROR: parser: parse error at or near "."
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Probably the grammar specifies just <column name> and not anything
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more complex after DISTINCT ON. It'd be risky to try to accept a
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general expression after ON, due to the silly decision to leave out
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any terminating punctuation.
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>> SELECT DISTINCT ON is not in SQL92, and I think it shouldn't be in
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>> Postgres either...
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> I'm not an SQL expert, but if it works and this feature is in standard
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> but only syntax is diffrent,
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No, there is no feature in SQL that allows DISTINCT on a subset of
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columns, period. This is not merely a matter of syntax, it's a
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fundamental semantic issue.
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> why just not to use standard
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>
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> select distinct(date), bytes from access_log;
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>
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> Or I'm missing here ?
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I don't think that does what you expect it to (hint: the
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parentheses are redundant).
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regards, tom lane
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From owner-pgsql-sql@hub.org Tue Jul 13 18:02:01 1999
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Tue, 13 Jul 1999 17:31:49 -0400 (EDT)
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To: Hannu Krosing <hannu@trust.ee>
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cc: hackers@postgreSQL.org, pgsql-sql@postgreSQL.org
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Subject: [SQL] Re: [HACKERS] SELECT DISTINCT question
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In-reply-to: Your message of Tue, 13 Jul 1999 23:50:57 +0300
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<378BA6B1.2B226DDB@trust.ee>
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Date: Tue, 13 Jul 1999 17:31:48 -0400
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Message-ID: <24413.931901508@sss.pgh.pa.us>
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Sender: owner-pgsql-sql@postgreSQL.org
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Precedence: bulk
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Status: ROr
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Hannu Krosing <hannu@trust.ee> writes:
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>> "DISTINCT will eliminate all duplicate rows from the selection.
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>> DISTINCT ON column will eliminate all duplicates in the specified column;
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>> this is equivalent to using GROUP BY column."
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> If it is equivalent to GROUP BY then it should allow only aggregates
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> in non-distinct columns, like:
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> select distinct on date date, sum(bytes) from access_log;
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> If it does not, then it should be files as a bug imho.
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It does not. Whether that is a bug is hard to say, since there is no
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standard I know of that says what it *is* supposed to do.
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If you look at the select_distinct_on regress test outputs, I bet you
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will be even less happy:
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QUERY: SELECT DISTINCT ON string4 two, string4, ten
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FROM tmp
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ORDER BY two using <, string4 using <, ten using <;
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two|string4|ten
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---+-------+---
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0|AAAAxx | 0
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0|HHHHxx | 0
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0|OOOOxx | 0
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0|VVVVxx | 0
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1|AAAAxx | 1
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1|HHHHxx | 1
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1|OOOOxx | 1
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1|VVVVxx | 1
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(8 rows)
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That's not exactly my idea of "distinct" values of string4 ---
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but apparently whoever made up the regress test thought it was OK!
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Can anyone defend this feature or provide a coherent definition
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of what it's supposed to be doing? My urge to rip it out is
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growing stronger and stronger...
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regards, tom lane
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From tgl@sss.pgh.pa.us Thu Sep 23 17:27:49 1999
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Thu, 23 Sep 1999 17:27:38 -0400 (EDT)
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To: Bruce Momjian <maillist@candle.pha.pa.us>
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cc: Hannu Krosing <hannu@trust.ee>, hackers@postgreSQL.org,
|
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pgsql-sql@postgreSQL.org
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Subject: Re: [SQL] Re: [HACKERS] SELECT DISTINCT question
|
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In-reply-to: Your message of Thu, 23 Sep 1999 13:18:18 -0400 (EDT)
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<199909231718.NAA19629@candle.pha.pa.us>
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Date: Thu, 23 Sep 1999 17:27:37 -0400
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Message-ID: <15767.938122057@sss.pgh.pa.us>
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Status: ROr
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Bruce Momjian <maillist@candle.pha.pa.us> writes:
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> Tom, any status on this DISTINCT ON ripout?
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I haven't done anything about it, if that's what you mean.
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I didn't get any indication of whether anyone else agreed with me
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(maybe the lack of loud complaints should be taken as consent?)
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regards, tom lane
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