Обсуждение: Counting distinct names
Let's say I have a table: table1 ===== subject_name text subject_age int4 test_trial int4 test_score int4 I'd like to find out how many times a unique 'subject_name' is in the table. My SQL book says that I should be able to do this: select COUNT(DISTINCT subject_name) from table1; However, the psql program is giving me an "ERROR: parser: parse error at or near "distinct"". Is there another way to do this (or a problem with my query)? Thanks. -Tony Reina Using [PostgreSQL 6.5.1 on i686-pc-linux-gnu, compiled by gcc egcs-2.91.66]
On Mon, 17 Apr 2000, G. Anthony Reina wrote: > Let's say I have a table: > > table1 > ===== > > subject_name text > subject_age int4 > test_trial int4 > test_score int4 > > > I'd like to find out how many times a unique 'subject_name' is in the > table. My SQL book says that I should be able to do this: > > select COUNT(DISTINCT subject_name) from table1; SELECT DISTINCT(subject_name), COUNT(subject_name) FROM table1 GROUP BY subject_name ; Brett W. McCoy http://www.chapelperilous.net --------------------------------------------------------------------------- Anything that is good and useful is made of chocolate.
"G. Anthony Reina" <reina@nsi.edu> writes:
> I'd like to find out how many times a unique 'subject_name' is in the
> table. My SQL book says that I should be able to do this:
> select COUNT(DISTINCT subject_name) from table1;
> However, the psql program is giving me an "ERROR: parser: parse error
> at or near "distinct"".
6.5 doesn't have aggregate(DISTINCT ...). 7.0 does, though.
If you don't want to upgrade right now, you could do something like
SELECT DISTINCT subject_name INTO temp_table FROM table1;
SELECT count(*) FROM temp_table;
DROP TABLE temp_table;
regards, tom lane
Tom Lane wrote: > "G. Anthony Reina" <reina@nsi.edu> writes: > > I'd like to find out how many times a unique 'subject_name' is in the > > table. My SQL book says that I should be able to do this: > > select COUNT(DISTINCT subject_name) from table1; > > However, the psql program is giving me an "ERROR: parser: parse error > > at or near "distinct"". > > 6.5 doesn't have aggregate(DISTINCT ...). 7.0 does, though. > > If you don't want to upgrade right now, you could do something like > > SELECT DISTINCT subject_name INTO temp_table FROM table1; > SELECT count(*) FROM temp_table; > DROP TABLE temp_table; > > regards, tom lane Thanks Tom. I'll eventually upgrade, but still am a little wary considering how many messages hackers continues to get on beta5. Perhaps, when 7.1 is out I'll feel a little more secure about the upgrade. -Tony
"G. Anthony Reina" <reina@nsi.edu> writes:
> Thanks Tom. I'll eventually upgrade, but still am a little wary considering
> how many messages hackers continues to get on beta5. Perhaps, when 7.1 is
> out I'll feel a little more secure about the upgrade.
You meant 7.0.1, no? 7.1 will be a new major release with its own bugs...
Seriously, despite the amount of traffic about 7.0 issues, I believe
that 7.0 beta is already considerably more reliable than any prior
release ever was; and I believe the other developers share that opinion.
If you think 6.5.* is bug-free then you haven't been paying attention ;-).
We've fixed a huge number of problems since 6.5. Furthermore, how are
we going to flush out remaining issues if people don't try it? You're
not doing yourself or anyone else a service by staying away from 7.0.
regards, tom lane
On Wed, 19 Apr 2000, Tom Lane wrote: > "G. Anthony Reina" <reina@nsi.edu> writes: > > Thanks Tom. I'll eventually upgrade, but still am a little wary considering > > how many messages hackers continues to get on beta5. Perhaps, when 7.1 is > > out I'll feel a little more secure about the upgrade. > > You meant 7.0.1, no? 7.1 will be a new major release with its own bugs... > > Seriously, despite the amount of traffic about 7.0 issues, I believe > that 7.0 beta is already considerably more reliable than any prior > release ever was; and I believe the other developers share that opinion. > If you think 6.5.* is bug-free then you haven't been paying attention ;-). > We've fixed a huge number of problems since 6.5. Furthermore, how are > we going to flush out remaining issues if people don't try it? You're > not doing yourself or anyone else a service by staying away from 7.0. OK, here are my comments and questions after just a very short play yesterday evening with 7.0RC1. ( should I be getting the snapshot? ) 1) There are files on the ftp sites which seem to be the "whole thing" and what I suppose is the "whole thing" cut up into smaller sections. Am I correct? Or do I need to d/l the smaller files as well? A README_for_Download might be a good idea. 2) I couldn't find a --database-dir=[/var/lib/pgsql/data] option in the output from ./configure --help. How can one configure pg to place it's database in a defined place in the file system? btw the default of /var/lib/pgsql/data seems pretty sensible. 3) Some of the scripts and binary files for the subsiduary tools have to be installed by hand. If you need to know what, I'd be happy to re-install pg and take notes. 4) For my tiny ultra-simple database it "just goes". ( On SuSE-6.3 ) 5) Is the idea of putting the data on a raw partition on the horizon? Thanks for a wonderful product. -- Sincerely etc., NAME Christopher Sawtell - iOpen Technologies Ltd.CELL PHONE 021 257 4451ICQ UIN 45863470EMAIL chris @ iopen. co . nz, csawtell @ xtra . co . nzWWW http://www.iopen.co.nzCNOTES ftp://ftp.funet.fi/pub/languages/C/tutorials/sawtell_C.tar.gz -->> Please refrain from using HTML or WORD attachments in e-mails to me <<--
Christopher Sawtell <csawtell@xtra.co.nz> writes:
> 1) There are files on the ftp sites which seem to be the "whole thing"
> and what I suppose is the "whole thing" cut up into smaller sections.
Yes.
> Am I correct? Or do I need to d/l the smaller files as well?
> A README_for_Download might be a good idea.
Yo, Marc ... where's the documentation about the new tarfile sections?
> 2) I couldn't find a --database-dir=[/var/lib/pgsql/data] option in
> the output from ./configure --help. How can one configure pg to place
> it's database in a defined place in the file system? btw the default
> of /var/lib/pgsql/data seems pretty sensible.
The default location is PREFIX/data; I don't think there is a configure
option to change that without setting --prefix. However, you can set it
at runtime with the -D options to initdb and postmaster, so adding yet
another configure switch might be gilding the lily.
> 3) Some of the scripts and binary files for the subsiduary tools have
> to be installed by hand. If you need to know what, I'd be happy to
> re-install pg and take notes.
News to me, other than that the perl interface module usually has to be
installed separately because of permission issues. What did you see
missing?
> 5) Is the idea of putting the data on a raw partition on the horizon?
Not really. There are portability issues with that; furthermore, it's
not obvious that it'd be better. The system's been developed and tuned
to sit atop a Unix kernel's disk cache. Writing our own disk management
code would be a large investment of work and a large loss of portability
for very questionable benefits. It might happen someday, but I think
we have many higher-priority tasks ahead...
regards, tom lane
On Wed, 19 Apr 2000, Tom Lane wrote: > > 2) I couldn't find a --database-dir=[/var/lib/pgsql/data] option in > > the output from ./configure --help. > The default location is PREFIX/data; I don't think there is a configure > option to change that without setting --prefix. That's news to me. There is no default for the data storage location anywhere that I can see. You always need to use the -D option or set PGDATA in the environment. Of course PREFIX/data is the commonly used place but it isn't any more special than any other location. -- Peter Eisentraut Sernanders väg 10:115 peter_e@gmx.net 75262 Uppsala http://yi.org/peter-e/ Sweden
Peter Eisentraut <e99re41@DoCS.UU.SE> writes:
> On Wed, 19 Apr 2000, Tom Lane wrote:
>> The default location is PREFIX/data; I don't think there is a configure
>> option to change that without setting --prefix.
> That's news to me. There is no default for the data storage location
> anywhere that I can see. You always need to use the -D option or set
> PGDATA in the environment.
Oh, you're right of course. My system behaves like there's a default,
but that's because I have PGDATA set in my .profile ;-)
*Should* there be a default location established by configure?
I think I'd prefer that to having the dependence on an environment var
... but on the other hand we couldn't really remove the envar without
breaking a lot of installations...
regards, tom lane
Tom Lane <tgl@sss.pgh.pa.us> writes: > *Should* there be a default location established by configure? I think so. > I think I'd prefer that to having the dependence on an environment var > ... but on the other hand we couldn't really remove the envar without > breaking a lot of installations... Keep the environment variable and let it override the default. The test suite could use a sane default for PGLIB too. It seems strange to compile and install postgres into a default location and then have `make runtest' fail due to an environment variable not being set. All the more so because the README file doesn't mention it.
SL Baur writes: > Tom Lane <tgl@sss.pgh.pa.us> writes: > > > *Should* there be a default location established by configure? > > I think so. I don't think so, see separate message. > The test suite could use a sane default for PGLIB too. That's a completely different issue, because the files obtained that way are necessarily fixed for a given installation (unless you are *very* crafty). Peeking at the GNU/Autoconf recommendations, the files in question should be installed into PREFIX/share by default and that default noted inside the using program (initdb), with overriding possible. Of course the name of the corresponding configure option --datadir isn't going to make our life easier vis a vis the first issue above, but it's still the way to go somehow. -- Peter Eisentraut Sernanders väg 10:115 peter_e@gmx.net 75262 Uppsala http://yi.org/peter-e/ Sweden
Tom Lane writes: > *Should* there be a default location established by configure? Not IMO. Firstly (broken record time), configure should not be used to set run-time options period. (And there's a single good reason for that: when users build a package they won't know what options they need later on. I get really annoyed at packages that do that.) Secondly, this will lead to all kinds of funny problem reports because everyone will have a different default. Worse yet, people might not even know what their default is because they use a binary package. I think the current setup is the cleanest by far because it emphasizes the independence of the data storage location and the fact that multiple locations are equally valid. > I think I'd prefer that to having the dependence on an environment var Environment variables are a common way of pointing programs to their data. Personally, I rarely bother with it and start the postmaster with -D instead, then I know what I'm getting. I suppose there's no reason that users couldn't do the same. The environment variable is only wildly useful if people start and stop the server all the time. -- Peter Eisentraut Sernanders väg 10:115 peter_e@gmx.net 75262 Uppsala http://yi.org/peter-e/ Sweden