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+ Sun, 11 Jul 1999 00:16:40 +0400 (MSD)
+Date: Sun, 11 Jul 1999 00:16:39 +0400 (MSD)
+X-Sender: megera@ra
+Subject: [SQL] SELECT DISTINCT question
+Organization: Sternberg Astronomical Institute (Moscow University)
+MIME-Version: 1.0
+Content-Type: TEXT/PLAIN; charset=US-ASCII
+Precedence: bulk
+Status: RO
+
+I got a problem with query:
+
+select distinct (date), bytes from access_log;
+
+which works but not as I expect. I thought this query will select
+all rows with distinct values of 'date' column, but it get
+distinct pairs 'date, bytes' . From documnetation I see
+
+"DISTINCT will eliminate all duplicate rows from the selection.
+DISTINCT ON column will eliminate all duplicates in the specified column;
+this is equivalent to using GROUP BY column.
+ALL will return all candidate rows, including duplicates."
+
+discovery=> select distinct on date,bytes from access_log;
+ERROR: parser: parse error at or near ","
+
+ Regards,
+
+ Oleg
+_____________________________________________________________
+Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
+Sternberg Astronomical Institute, Moscow University (Russia)
+phone: +007(095)939-16-83, +007(095)939-23-83
+
+
+
+
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+ Sat, 10 Jul 1999 17:18:28 -0400 (EDT)
+Subject: [SQL] Re: [HACKERS] SELECT DISTINCT question
+In-reply-to: Your message of Sun, 11 Jul 1999 00:16:39 +0400 (MSD)
+Date: Sat, 10 Jul 1999 17:18:28 -0400
+From: Tom Lane
+Precedence: bulk
+Status: RO
+
+> discovery=> select distinct on date,bytes from access_log;
+> ERROR: parser: parse error at or near ","
+
+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;
+
+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...
+
+ regards, tom lane
+
+
+ by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id MAA26263
+ for ; Sun, 11 Jul 1999 12:01:22 -0400 (EDT)
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+ Sun, 11 Jul 1999 10:09:24 +0400 (MSD)
+Date: Sun, 11 Jul 1999 10:09:24 +0400 (MSD)
+X-Sender: megera@ra
+To: Tom Lane
+Subject: Re: [SQL] Re: [HACKERS] SELECT DISTINCT question
+Organization: Sternberg Astronomical Institute (Moscow University)
+MIME-Version: 1.0
+Content-Type: TEXT/PLAIN; charset=US-ASCII
+Precedence: bulk
+Status: RO
+
+On Sat, 10 Jul 1999, Tom Lane wrote:
+
+> Date: Sat, 10 Jul 1999 17:18:28 -0400
+> From: Tom Lane
+> Subject: [SQL] Re: [HACKERS] SELECT DISTINCT question
+>
+> > discovery=> select distinct on date,bytes from access_log;
+> > ERROR: parser: parse error at or near ","
+>
+> 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
+>
+
+_____________________________________________________________
+Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
+Sternberg Astronomical Institute, Moscow University (Russia)
+phone: +007(095)939-16-83, +007(095)939-23-83
+
+
+
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+ Sun, 11 Jul 1999 10:09:24 +0400 (MSD)
+Date: Sun, 11 Jul 1999 10:09:24 +0400 (MSD)
+X-Sender: megera@ra
+To: Tom Lane
+Subject: Re: [SQL] Re: [HACKERS] SELECT DISTINCT question
+Organization: Sternberg Astronomical Institute (Moscow University)
+MIME-Version: 1.0
+Content-Type: TEXT/PLAIN; charset=US-ASCII
+Precedence: bulk
+Status: RO
+
+On Sat, 10 Jul 1999, Tom Lane wrote:
+
+> Date: Sat, 10 Jul 1999 17:18:28 -0400
+> From: Tom Lane
+> Subject: [SQL] Re: [HACKERS] SELECT DISTINCT question
+>
+> > discovery=> select distinct on date,bytes from access_log;
+> > ERROR: parser: parse error at or near ","
+>
+> 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
+>
+
+_____________________________________________________________
+Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
+Sternberg Astronomical Institute, Moscow University (Russia)
+phone: +007(095)939-16-83, +007(095)939-23-83
+
+
+
+ by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id MAA26248
+ for ; Sun, 11 Jul 1999 12:01:15 -0400 (EDT)
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+ Sun, 11 Jul 1999 11:38:44 -0400 (EDT)
+Subject: Re: [SQL] Re: [HACKERS] SELECT DISTINCT question
+In-reply-to: Your message of Sun, 11 Jul 1999 10:09:24 +0400 (MSD)
+Date: Sun, 11 Jul 1999 11:38:43 -0400
+From: Tom Lane
+Precedence: bulk
+Status: RO
+
+> 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 "."
+
+Probably the grammar specifies just and not anything
+more complex after DISTINCT ON. It'd be risky to try to accept a
+general expression after ON, due to the silly decision to leave out
+any terminating punctuation.
+
+>> 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,
+
+No, there is no feature in SQL that allows DISTINCT on a subset of
+columns, period. This is not merely a matter of syntax, it's a
+fundamental semantic issue.
+
+> why just not to use standard
+>
+> select distinct(date), bytes from access_log;
+>
+> Or I'm missing here ?
+
+I don't think that does what you expect it to (hint: the
+parentheses are redundant).
+
+ regards, tom lane
+
+
+ by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id SAA07953
+ for ; Tue, 13 Jul 1999 18:02:00 -0400 (EDT)
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+ Tue, 13 Jul 1999 17:31:49 -0400 (EDT)
+To: Hannu Krosing
+Subject: [SQL] Re: [HACKERS] SELECT DISTINCT question
+In-reply-to: Your message of Tue, 13 Jul 1999 23:50:57 +0300
+Date: Tue, 13 Jul 1999 17:31:48 -0400
+From: Tom Lane
+Precedence: bulk
+Status: ROr
+
+Hannu Krosing writes:
+>> "DISTINCT will eliminate all duplicate rows from the selection.
+>> DISTINCT ON column will eliminate all duplicates in the specified column;
+>> this is equivalent to using GROUP BY column."
+
+> If it is equivalent to GROUP BY then it should allow only aggregates
+> in non-distinct columns, like:
+> select distinct on date date, sum(bytes) from access_log;
+> If it does not, then it should be files as a bug imho.
+
+It does not. Whether that is a bug is hard to say, since there is no
+standard I know of that says what it *is* supposed to do.
+
+If you look at the select_distinct_on regress test outputs, I bet you
+will be even less happy:
+
+QUERY: SELECT DISTINCT ON string4 two, string4, ten
+ FROM tmp
+ ORDER BY two using <, string4 using <, ten using <;
+two|string4|ten
+---+-------+---
+ 0|AAAAxx | 0
+ 0|HHHHxx | 0
+ 0|OOOOxx | 0
+ 0|VVVVxx | 0
+ 1|AAAAxx | 1
+ 1|HHHHxx | 1
+ 1|OOOOxx | 1
+ 1|VVVVxx | 1
+(8 rows)
+
+That's not exactly my idea of "distinct" values of string4 ---
+but apparently whoever made up the regress test thought it was OK!
+
+Can anyone defend this feature or provide a coherent definition
+of what it's supposed to be doing? My urge to rip it out is
+growing stronger and stronger...
+
+ regards, tom lane
+
+
+Received: from sss.sss.pgh.pa.us (sss.pgh.pa.us [209.114.166.2])
+ by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id RAA25975
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+ Thu, 23 Sep 1999 17:27:38 -0400 (EDT)
+To: Bruce Momjian
+Subject: Re: [SQL] Re: [HACKERS] SELECT DISTINCT question
+In-reply-to: Your message of Thu, 23 Sep 1999 13:18:18 -0400 (EDT)
+Date: Thu, 23 Sep 1999 17:27:37 -0400
+From: Tom Lane
+Status: ROr
+
+Bruce Momjian writes:
+> Tom, any status on this DISTINCT ON ripout?
+
+I haven't done anything about it, if that's what you mean.
+
+I didn't get any indication of whether anyone else agreed with me
+(maybe the lack of loud complaints should be taken as consent?)
+
+ regards, tom lane
+
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