[GENERAL] dynamic crosstab
Hello everybody, I'm trying to find out how to have a dynamic crosstab as in excel, ireport,etc... As i understand of the manual here : http://docs.postgresqlfr.org/8.4/tablefunc.html I can have multiple columns. Unfortunately, it seems indispensible to name the columns in the AS clause. Am I right or is ther a way to let the query generate the columns and there name without naming them? Best regards Florent THOMAS
Re: [GENERAL] dynamic crosstab
On 01/31/2010 03:52 PM, Florent THOMAS wrote: Hello everybody, I'm trying to find out how to have a dynamic crosstab as in excel, ireport,etc... As i understand of the manual here : http://docs.postgresqlfr.org/8.4/tablefunc.html I can have multiple columns. Unfortunately, it seems indispensible to name the columns in the AS clause. Am I right or is ther a way to let the query generate the columns and there name without naming them? Wow, second time this week this has come up. Maybe it ought to be an FAQ. Anyway, your best bet is to use crosstab from contrib/tablefunc, and wrap it with application code that dynamically executes the query with the needed column definitions. It is a simple two step process: Using crosstab(text source_sql, text category_sql), - first execute category_sql to get a list of columns - dynamically build the complete crosstab SQL including the columns - execute the crosstab SQL The parser/planner requires the column type information because the result is potentially filtered (WHERE clause) or joined (FROM CLAUSE) with other relations. There is no way around this, at least not currently, and probably not ever in this form. If PostgreSQL ever supports true procedures (i.e. CALL sp_crosstab(...)), then it would be possible to forego the column definitions as joining and filtering would not be possible in that scenario. Joe signature.asc Description: OpenPGP digital signature
Re: [GENERAL] dynamic crosstab
On 1/28/2010 5:51 PM, Pierre Chevalier wrote:
while ( my @list = $get-fetchrow_array)
{
print join(',', @list), \n;
}
It throws some insulting messages, though:
Use of uninitialized value $list[5] in join or string at
./crosstab_perl.pl line 24.
Use of uninitialized value $list[6] in join or string at
./crosstab_perl.pl line 24.
Use of uninitialized value $list[7] in join or string at
./crosstab_perl.pl line 24.
Yeah, you can ignore them. Fields that are null in the database will be
converted to undef in perl, which when printed spits out that warning.
Right before the print, we could test for undef and set them to empty
string like:
map { if (!defined($_)) {$_ = '';}} @list;
so the while loop would look like:
while ( my @list = $get-fetchrow_array)
{
map { if (!defined($_)) {$_ = '';}} @list;
print join(',', @list), \n;
}
-Andy
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Re: [GENERAL] dynamic crosstab
On 1/27/2010 3:49 AM, Pierre Chevalier wrote: Pavel Stehule claviota: ... But what I would like to do is to redirect the output of the function (that is, the 'result' cursor) to a view, which will be used in other places. I thought something like FETCH INTO would do the trick, but it doesn't. Also, I need, at some point, to export the output to some CSV file. I usually do a quick bash script as follows: echo COPY (SELECT * FROM dh_litho ORDER BY id, depto) TO stdout WITH CSV HEADER; | psql bdexplo somefile.csv ... hmm ...it cannot work :(. You cannot forward FETCH ALL statement on server side - without programming in C Ach! Too bad... Oh but... I used to program in C, long time ago, on HP-UX... How do you feel about a little perl? It would be pretty simple, and could generate a csv based on any resultset (any number of columns). I'd be happy to post a little get you started code if you wanted. -Andy -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
On 1/28/2010 9:11 AM, Andy Colson wrote:
On 1/27/2010 3:49 AM, Pierre Chevalier wrote:
Pavel Stehule claviota:
...
But what I would like to do is to redirect the output of the function
(that
is, the 'result' cursor) to a view, which will be used in other
places. I
thought something like FETCH INTO would do the trick, but it doesn't.
Also, I need, at some point, to export the output to some CSV file. I
usually do a quick bash script as follows:
echo COPY (SELECT * FROM dh_litho ORDER BY id, depto) TO stdout WITH
CSV
HEADER; | psql bdexplo somefile.csv
...
hmm ...it cannot work :(. You cannot forward FETCH ALL statement on
server side - without programming in C
Ach! Too bad... Oh but... I used to program in C, long time ago, on
HP-UX...
How do you feel about a little perl? It would be pretty simple, and
could generate a csv based on any resultset (any number of columns). I'd
be happy to post a little get you started code if you wanted.
-Andy
Humm... a comma, or quotes, would have made that make sense:
be happy to post a little get you started code if you wanted.
here's some code, its based on Pavel's example, and dumps csv to stdout:
#!/usr/bin/perl
use strict;
use warnings;
use DBI;
my $db = DBI-connect(dbi:Pg:dbname=andy, 'andy', '', {AutoCommit =
0, RaiseError = 1});
$db-do(EOS);
SELECT do_cross_cursor('shop', 'FROM shops','gender','FROM employees e
JOIN shops s ON s.id = e.shop_id',
'salary')
EOS
my $get = $db-prepare('FETCH ALL FROM result');
$get-execute;
my $names = $get-{'NAME'};
print join(',', @$names), \n;
while ( my @list = $get-fetchrow_array)
{
print join(',', @list), \n;
}
$get = undef;
$db-do('commit');
$db-disconnect;
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Re: [GENERAL] dynamic crosstab
On 01/28/2010 08:57 AM, Andy Colson wrote: How do you feel about a little perl? It would be pretty simple, and could generate a csv based on any resultset (any number of columns). I'd be happy to post a little get you started code if you wanted. If you're going to go through all that, I don't understand why you wouldn't just use crosstab from contrib/tablefunc, and wrap it with application code that dynamically executes the query with the needed column definitions. It is a simple two step process: Using crosstab(text source_sql, text category_sql), - first execute category_sql to get a list of columns - build the complete crosstab SQL including the columns - execute the crosstab SQL The fact is that, as has been stated, the parser/planner requires the column type information because the result is potentially filtered or joined with other relations. There is no way around this, at least not currently, and probably not ever in this form. If PostgreSQL ever supports true procedures (i.e. CALL sp_crosstab(...)), then it would be possible to forego the column definitions as joining and filtering are not possible. Joe signature.asc Description: OpenPGP digital signature
Re: [GENERAL] dynamic crosstab
Pavel Stehule claviota: Nut... Idea! (careful...) what about if we do, just like in a VIEW, a CREATE OR REPLACE, systematically when we do this kind of function? The only drawback I can think of is that we can't have anything dependant on the VIEW we generate. no, you cannot do it. You cannot create view and same statements ask on this view on top level. if you would to understand it - you have to understand to process pipeline: parser, planner, optimizer, executor. If you understand to this stages, then you will understand what is possible and what not. Ok, ok. I just imagine, for now... I guess I have to swallow a big bunch of doc and code before I can really understand this, so I take your word. Another idea (more danger...): what about setting a sort of flag which says that this VIEW should *not* be included in the planner? And it will have unexpected number of columns? Would this be *absolutely* impossible to state? :) sorry - you can do it, but not in pg - or you have to rewrite 50% of low level code Oh well, not tonight... ;) look on SPI interface http://www.postgresql.org/docs/8.4/interactive/spi.html http://www.postgresql.org/docs/8.4/interactive/spi-examples.html but you have to use cursor based interface. I'll try to Read The French Manual, rather than the one in English! I'll look for it... But the whole point is: this need of a generic cross-tab is really annoying for a large number of people, it has been there for a long time, and I know some people who just walk away from postgreSQL only because this feature is lacking, and they return happily to their m$-access, therefore ignoring the pure wealth of postgreSQL: sad, isn't it?... ms access hasn't klient-server architecture. Generating of crosstab is client side task - more - iOLTP databases are not the best tool for it. Better are OLAP databases with GUI clients - like Excel or MS Access. OK, I got your point. Thanks for explaining patiently! In fact, what I wanted to do within postgresql, I'd better try to do it somewhere else, with a client more in an OLAP style. I got so used to do *everything* inside postgresql (well, through psql), complex queries, nested things, with visual graphs generated by queries... that I thought it was just endless! Oh well, this is the limit. Now, talking about GUI clients: I've been looking for a long time for a decent tool that could replace an access, to interact with my postgresql database. So far, the best I found is knoda, for my needs. I battled a bit with oobase, not very convincing, or I missed something. Apparently, as I can google, quite a few projects have been abandoned. Does someone knwo if there something new, on this side? I'm also quite nostalgique (English?) of dBase IV, and its screens, forms and tables with the F4 key... I was wandering whether a project of an ncurses-based front-end for postgreql (actually, it could be for any FLOSS database, I guess) could be developed: again, does someone know if such a project exists? -- Pierre Chevalier Mesté Duran 32100 Condom Tél : 09 75 27 45 62 - 06 37 80 33 64 http://pierremariechevalier.free.fr/ Logiciels Libres dans le Gers: http://gnusquetaires.org/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
Andy Colson claviota: Ach! Too bad... Oh but... I used to program in C, long time ago, on HP-UX... How do you feel about a little perl? Hm, I am not too familiar with perl. That's the least I can say. But, after all, why not? It would be pretty simple, and could generate a csv Actually, I would have liked to have something that I can reuse within postgresql, just like a view. Sorry, I'm an idealist... based on any resultset (any number of columns). I'd be happy to post a little get you started code if you wanted. Sure, why not? Thanks! -- Pierre Chevalier Mesté Duran 32100 Condom Tél : 09 75 27 45 62 - 06 37 80 33 64 http://pierremariechevalier.free.fr/ Logiciels Libres dans le Gers: http://gnusquetaires.org/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
Andy Colson claviota:
...
be happy to post a little get you started code if you wanted.
here's some code, its based on Pavel's example, and dumps csv to stdout:
Hmm, pretty cryptic to my eyes...
Thanks for not writing everything on one line!
#!/usr/bin/perl
use strict;
use warnings;
use DBI;
my $db = DBI-connect(dbi:Pg:dbname=andy, 'andy', '', {AutoCommit =
0, RaiseError = 1});
$db-do(EOS);
SELECT do_cross_cursor('shop', 'FROM shops','gender','FROM employees e
JOIN shops s ON s.id = e.shop_id',
'salary')
EOS
my $get = $db-prepare('FETCH ALL FROM result');
$get-execute;
my $names = $get-{'NAME'};
print join(',', @$names), \n;
while ( my @list = $get-fetchrow_array)
{
print join(',', @list), \n;
}
$get = undef;
$db-do('commit');
$db-disconnect;
OK, I think I got the point: instead of working from psql, you just call
the function from outside, and you walk through the resulting dataset,
adding commas and returns when needed.
I 've just tried it with my data: it works! ;)
It throws some insulting messages, though:
Use of uninitialized value $list[5] in join or string at
./crosstab_perl.pl line 24.
Use of uninitialized value $list[6] in join or string at
./crosstab_perl.pl line 24.
Use of uninitialized value $list[7] in join or string at
./crosstab_perl.pl line 24.
...
But the .csv file is there, after a redirection, and it seems fine! I'm
just worried about the messages: anything serious, or can I just ignore
them?
I'll do a diff with the csv I generated before (with psql, \a, and some
sed...)
Thanks a lot!
A+
Pierre
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Re: [GENERAL] dynamic crosstab
2010/1/29 Pierre Chevalier pierre.chevalier1...@free.fr: Pavel Stehule claviota: Nut... Idea! (careful...) what about if we do, just like in a VIEW, a CREATE OR REPLACE, systematically when we do this kind of function? The only drawback I can think of is that we can't have anything dependant on the VIEW we generate. no, you cannot do it. You cannot create view and same statements ask on this view on top level. if you would to understand it - you have to understand to process pipeline: parser, planner, optimizer, executor. If you understand to this stages, then you will understand what is possible and what not. Ok, ok. I just imagine, for now... I guess I have to swallow a big bunch of doc and code before I can really understand this, so I take your word. Another idea (more danger...): what about setting a sort of flag which says that this VIEW should *not* be included in the planner? And it will have unexpected number of columns? Would this be *absolutely* impossible to state? :) sorry - you can do it, but not in pg - or you have to rewrite 50% of low level code Oh well, not tonight... ;) look on SPI interface http://www.postgresql.org/docs/8.4/interactive/spi.html http://www.postgresql.org/docs/8.4/interactive/spi-examples.html but you have to use cursor based interface. I'll try to Read The French Manual, rather than the one in English! I'll look for it... But the whole point is: this need of a generic cross-tab is really annoying for a large number of people, it has been there for a long time, and I know some people who just walk away from postgreSQL only because this feature is lacking, and they return happily to their m$-access, therefore ignoring the pure wealth of postgreSQL: sad, isn't it?... ms access hasn't klient-server architecture. Generating of crosstab is client side task - more - iOLTP databases are not the best tool for it. Better are OLAP databases with GUI clients - like Excel or MS Access. OK, I got your point. Thanks for explaining patiently! In fact, what I wanted to do within postgresql, I'd better try to do it somewhere else, with a client more in an OLAP style. I got so used to do *everything* inside postgresql (well, through psql), complex queries, nested things, with visual graphs generated by queries... that I thought it was just endless! Oh well, this is the limit. I like this strategy too. But I think - and it is important limit. PostgreSQL is OLTP database. It isn't OLAP database or ROLAP database. If you like do some interactive analyses (on larger dataset) - you need minimally different server (because slow query can shots performance), you need some specialised sw - there are lot of sw better than postgres for this - Mondrian, Pentaho, olap4j. Now, talking about GUI clients: I've been looking for a long time for a decent tool that could replace an access, to interact with my postgresql database. So far, the best I found is knoda, for my needs. I battled a bit with oobase, not very convincing, or I missed something. Apparently, as I can google, quite a few projects have been abandoned. Does someone knwo if there something new, on this side? I'm also quite nostalgique (English?) of dBase IV, and its screens, forms and tables with the F4 key... I was wandering whether a project of an ncurses-based front-end for postgreql (actually, it could be for any FLOSS database, I guess) could be developed: again, does someone know if such a project exists? sorry. I don't know about any Regards Pavel Stehule -- Pierre Chevalier Mesté Duran 32100 Condom Tél : 09 75 27 45 62 - 06 37 80 33 64 http://pierremariechevalier.free.fr/ Logiciels Libres dans le Gers: http://gnusquetaires.org/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
Hello,
Pavel Stehule claviota:
...
you cannot get crosstab via SELECT statement. There is workaround
http://okbob.blogspot.com/2008/08/using-cursors-for-generating-cross.html
All right, I've just tried it: it works just fine in my case! Thanks a lot!
Except a few things, but I am not (yet) familiar at all with postgresql
functions.
I have tried to customize a bit your function, tu suit some of my needs:
- when I have NULL values in my EAV (Entity-Attribute-Value) table, I
don't want zeroes to appear in the output table;
- the total at the right end does not make sense in my case; I replaced
it with a COUNT;
therefore, I did as follows (changes are *inside stars*, I hope the
formatting will work!):
BEGIN
FOR r IN EXECUTE 'SELECT DISTINCT '
|| dimx_name || '::text AS val ' || dimx_source
LOOP
col_list := array_append(col_list, 'SUM(CASE ' || dimx_name
|| ' WHEN ' || quote_literal(r.val) || ' THEN ' || expr
|| ' ELSE *NULL* END) AS ' || quote_ident(r.val) || '');
END LOOP;
query := 'SELECT ' || dimy_name || ', '
|| array_to_string(col_list, ',')
* || ', COUNT(' || expr || ') AS Count '*
|| dimy_source || ' GROUP BY ' || dimy_name;
OPEN result NO SCROLL FOR EXECUTE query;
RETURN result;
END;
$$ LANGUAGE plpgsql STRICT;
Now, I still have some issues: as far as I can remember, in m$ access
(yes, I know...), a long time ago, I used to do PIVOT queries on EAV
tables, where I could chose which operation was to be made on the
variable: simply the value (without GROUPing), or a SUM, AVG, etc. I
don't have any running acce$$ handy, so I can't check this, I'm afraid.
In the case of your function, if I understand well, the line with the
GROUP BY does the trick. I will try to play with it. Later on.
Something else: I am quite familiar with strict SQL, I use postgreSQL a
lot, but I am not familiar with functions and, also, cursors. So I am a
bit surprised by the behaviour of the cursor: I am reading doc...
But what I would like to do is to redirect the output of the function
(that is, the 'result' cursor) to a view, which will be used in other
places. I thought something like FETCH INTO would do the trick, but it
doesn't.
Also, I need, at some point, to export the output to some CSV file. I
usually do a quick bash script as follows:
echo COPY (SELECT * FROM dh_litho ORDER BY id, depto) TO stdout WITH
CSV HEADER; | psql bdexplo somefile.csv
And then I can feed somefile.csv to whatever program I want. I tried to
do this with the cursor and the FETCH ALL, but it didn't work out well,
as I had guessed...
pie...@duran:~$ pie...@duran:~/fix_bd_amc$ echo COPY (
SELECT do_cross_cursor('lab_pjcsa_analytecode', 'FROM
lab_ana_results','sample_id',
'FROM lab_ana_results_sel ',
'value_num');
FETCH ALL FROM result WITH CSV HEADER;
) TO stdout WITH CSV HEADER ; | psql bdexplo
bash: pie...@duran:~/fix_bd_amc$: Aucun fichier ou dossier de ce type
pie...@duran:~$ ERREUR: erreur de syntaxe sur ou près de « ; »
bash: ERREUR: : commande introuvable
bash: » : commande introuvable
pie...@duran:~$ LIGNE 4 : 'value_num');
bash: Erreur de syntaxe près du symbole inattendu « ) »
pie...@duran:~$ ^
bash: ^ : commande introuvable
(sorry about the French!)
I could not do this trick: any idea of how I could do this? I guess I
should wrap the whole transaction into a one-line statement to be fed to
to psql, but I can't figure out how to do it... Some help?
A+
Pierre
PS: I am used to normal mailing lists, but I got quite confused by the
approach from grokbase: I thought I was posting on the grokbase list
(http://grokbase.com/), and I see that the list
pgsql-general@postgresql.org was the one I was posting to...
Sorry for the noise, I am RTFMing at the moment...
--
Pierre Chevalier
Mesté Duran
32100 Condom
Tél+fax :09 75 27 45 62
05 62 28 06 83
06 37 80 33 64
Émail: pierre.chevalier1967CHEZfree.fr
icq# : 10432285
http://pierremariechevalier.free.fr/
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Re: [GENERAL] dynamic crosstab
2010/1/27 Pierre Chevalier pierre.chevalier1...@free.fr:
Hello,
Pavel Stehule claviota:
...
you cannot get crosstab via SELECT statement. There is workaround
http://okbob.blogspot.com/2008/08/using-cursors-for-generating-cross.html
All right, I've just tried it: it works just fine in my case! Thanks a lot!
Except a few things, but I am not (yet) familiar at all with postgresql
functions.
I have tried to customize a bit your function, tu suit some of my needs:
- when I have NULL values in my EAV (Entity-Attribute-Value) table, I don't
want zeroes to appear in the output table;
- the total at the right end does not make sense in my case; I replaced it
with a COUNT;
therefore, I did as follows (changes are *inside stars*, I hope the
formatting will work!):
BEGIN
FOR r IN EXECUTE 'SELECT DISTINCT '
|| dimx_name || '::text AS val ' || dimx_source
LOOP
col_list := array_append(col_list, 'SUM(CASE ' || dimx_name
|| ' WHEN ' || quote_literal(r.val) || ' THEN ' || expr
|| ' ELSE *NULL* END) AS ' || quote_ident(r.val) || '');
END LOOP;
query := 'SELECT ' || dimy_name || ', '
|| array_to_string(col_list, ',')
* || ', COUNT(' || expr || ') AS Count '*
|| dimy_source || ' GROUP BY ' || dimy_name;
OPEN result NO SCROLL FOR EXECUTE query;
RETURN result;
END;
$$ LANGUAGE plpgsql STRICT;
Now, I still have some issues: as far as I can remember, in m$ access (yes,
I know...), a long time ago, I used to do PIVOT queries on EAV tables, where
I could chose which operation was to be made on the variable: simply the
value (without GROUPing), or a SUM, AVG, etc. I don't have any running
acce$$ handy, so I can't check this, I'm afraid.
In the case of your function, if I understand well, the line with the GROUP
BY does the trick. I will try to play with it. Later on.
Something else: I am quite familiar with strict SQL, I use postgreSQL a lot,
but I am not familiar with functions and, also, cursors. So I am a bit
surprised by the behaviour of the cursor: I am reading doc...
But what I would like to do is to redirect the output of the function (that
is, the 'result' cursor) to a view, which will be used in other places. I
thought something like FETCH INTO would do the trick, but it doesn't.
Also, I need, at some point, to export the output to some CSV file. I
usually do a quick bash script as follows:
echo COPY (SELECT * FROM dh_litho ORDER BY id, depto) TO stdout WITH CSV
HEADER; | psql bdexplo somefile.csv
And then I can feed somefile.csv to whatever program I want. I tried to do
this with the cursor and the FETCH ALL, but it didn't work out well, as I
had guessed...
hmm ...it cannot work :(. You cannot forward FETCH ALL statement on
server side - without programming in C
in this case you need small application for reading cursor and
transformation to CVS
Pavel
pie...@duran:~$ pie...@duran:~/fix_bd_amc$ echo COPY (
SELECT do_cross_cursor('lab_pjcsa_analytecode', 'FROM
lab_ana_results','sample_id',
'FROM lab_ana_results_sel ',
'value_num');
FETCH ALL FROM result WITH CSV HEADER;
) TO stdout WITH CSV HEADER ; | psql bdexplo
bash: pie...@duran:~/fix_bd_amc$: Aucun fichier ou dossier de ce type
pie...@duran:~$ ERREUR: erreur de syntaxe sur ou près de « ; »
bash: ERREUR: : commande introuvable
bash: » : commande introuvable
pie...@duran:~$ LIGNE 4 : 'value_num');
bash: Erreur de syntaxe près du symbole inattendu « ) »
pie...@duran:~$ ^
bash: ^ : commande introuvable
(sorry about the French!)
I could not do this trick: any idea of how I could do this? I guess I should
wrap the whole transaction into a one-line statement to be fed to to psql,
but I can't figure out how to do it... Some help?
A+
Pierre
PS: I am used to normal mailing lists, but I got quite confused by the
approach from grokbase: I thought I was posting on the grokbase list
(http://grokbase.com/), and I see that the list pgsql-general@postgresql.org
was the one I was posting to...
Sorry for the noise, I am RTFMing at the moment...
--
Pierre Chevalier
Mesté Duran
32100 Condom
Tél+fax : 09 75 27 45 62
05 62 28 06 83
06 37 80 33 64
Émail : pierre.chevalier1967CHEZfree.fr
icq# : 10432285
http://pierremariechevalier.free.fr/
Logiciels Libres dans le Gers: http://gnusquetaires.org/
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Re: [GENERAL] dynamic crosstab
2010/1/27 Pierre Chevalier pierre.chevalier1...@free.fr: Pavel Stehule claviota: ... But what I would like to do is to redirect the output of the function (that is, the 'result' cursor) to a view, which will be used in other places. I thought something like FETCH INTO would do the trick, but it doesn't. Also, I need, at some point, to export the output to some CSV file. I usually do a quick bash script as follows: echo COPY (SELECT * FROM dh_litho ORDER BY id, depto) TO stdout WITH CSV HEADER; | psql bdexplo somefile.csv ... hmm ...it cannot work :(. You cannot forward FETCH ALL statement on server side - without programming in C Ach! Too bad... Oh but... I used to program in C, long time ago, on HP-UX... in this case you need small application for reading cursor and transformation to CVS Actually, if the small application was reading cursor, and transforming it to a VIEW, this would solve both problems at once: something like: CREATE VIEW crosstabbed_thing AS (cursor_to_dataset(SELECT do_cross_cursor(...))); no it isn't possible. VIEW have to have fixed numbers of columns. You can write function that reads a cursor, create temp table, store result and will do a copy from temp table. There is one significant rule - any SELECT based statement have to have known number of columns in planner time - so number of colums must not depend on the data. There are no any workaround for it. You can do only don't use fixed SELECT statemens (VIEWS too - it is stored SELECT). look on SPI interface http://www.postgresql.org/docs/8.4/interactive/spi.html http://www.postgresql.org/docs/8.4/interactive/spi-examples.html but you have to use cursor based interface. Pavel And then: echo COPY (SELECT * FROM crosstabbed_thing) TO stdout WITH CSV HEADER; | psql youpi.csv And there we are! What about this plan? The cursor_to_dataset() should be written, in C if I understand well. I have to dig out my old C book, and browse through postgresql APIs, code examples,etc. I guess... A+ Pierre -- Pierre Chevalier Mesté Duran 32100 Condom Tél+fax : 09 75 27 45 62 05 62 28 06 83 06 37 80 33 64 Émail : pierre.chevalier1967CHEZfree.fr icq# : 10432285 http://pierremariechevalier.free.fr/ Logiciels Libres dans le Gers: http://gnusquetaires.org/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
2010/1/27 Pierre Chevalier pierre.chevalier1...@free.fr: Pavel Stehule claviota: ... Actually, if the small application was reading cursor, and transforming it to a VIEW, this would solve both problems at once: something like: CREATE VIEW crosstabbed_thing AS (cursor_to_dataset(SELECT do_cross_cursor(...))); no it isn't possible. VIEW have to have fixed numbers of columns. Ach, flute... ;-( You can write function that reads a cursor, create temp table, store result and will do a copy from temp table. Well... Not extremely elegant (it reminds me when I was stuck with access and I could not do nested queries...), but why not? Actually, if the table is a real temporary one (CREATE TEMPORARY TABLE), it should not induce too much mess in the database layout. There is one significant rule - any SELECT based statement have to have known number of columns in planner time - so number of colums must not depend on the data. There are no any workaround for it. You can do only don't use fixed SELECT statemens (VIEWS too - it is stored SELECT). All right, it makes sense now... Nut... Idea! (careful...) what about if we do, just like in a VIEW, a CREATE OR REPLACE, systematically when we do this kind of function? The only drawback I can think of is that we can't have anything dependant on the VIEW we generate. no, you cannot do it. You cannot create view and same statements ask on this view on top level. if you would to understand it - you have to understand to process pipeline: parser, planner, optimizer, executor. If you understand to this stages, then you will understand what is possible and what not. Another idea (more danger...): what about setting a sort of flag which says that this VIEW should *not* be included in the planner? And it will have unexpected number of columns? Would this be *absolutely* impossible to state? :) sorry - you can do it, but not in pg - or you have to rewrite 50% of low level code look on SPI interface http://www.postgresql.org/docs/8.4/interactive/spi.html http://www.postgresql.org/docs/8.4/interactive/spi-examples.html but you have to use cursor based interface. I'll try to Read The French Manual, rather than the one in English! I'll look for it... But the whole point is: this need of a generic cross-tab is really annoying for a large number of people, it has been there for a long time, and I know some people who just walk away from postgreSQL only because this feature is lacking, and they return happily to their m$-access, therefore ignoring the pure wealth of postgreSQL: sad, isn't it?... ms access hasn't klient-server architecture. Generating of crosstab is client side task - more - iOLTP databases are not the best tool for it. Better are OLAP databases with GUI clients - like Excel or MS Access. Regards Pavel Stehule A+ Pierre -- Pierre Chevalier Mesté Duran 32100 Condom Tél+fax : 09 75 27 45 62 05 62 28 06 83 06 37 80 33 64 Émail : pierre.chevalier1967CHEZfree.fr icq# : 10432285 http://pierremariechevalier.free.fr/ Logiciels Libres dans le Gers: http://gnusquetaires.org/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
Pavel Stehule claviota: ... Actually, if the small application was reading cursor, and transforming it to a VIEW, this would solve both problems at once: something like: CREATE VIEW crosstabbed_thing AS (cursor_to_dataset(SELECT do_cross_cursor(...))); no it isn't possible. VIEW have to have fixed numbers of columns. Ach, flute... ;-( You can write function that reads a cursor, create temp table, store result and will do a copy from temp table. Well... Not extremely elegant (it reminds me when I was stuck with access and I could not do nested queries...), but why not? Actually, if the table is a real temporary one (CREATE TEMPORARY TABLE), it should not induce too much mess in the database layout. There is one significant rule - any SELECT based statement have to have known number of columns in planner time - so number of colums must not depend on the data. There are no any workaround for it. You can do only don't use fixed SELECT statemens (VIEWS too - it is stored SELECT). All right, it makes sense now... Nut... Idea! (careful...) what about if we do, just like in a VIEW, a CREATE OR REPLACE, systematically when we do this kind of function? The only drawback I can think of is that we can't have anything dependant on the VIEW we generate. Another idea (more danger...): what about setting a sort of flag which says that this VIEW should *not* be included in the planner? And it will have unexpected number of columns? Would this be *absolutely* impossible to state? look on SPI interface http://www.postgresql.org/docs/8.4/interactive/spi.html http://www.postgresql.org/docs/8.4/interactive/spi-examples.html but you have to use cursor based interface. I'll try to Read The French Manual, rather than the one in English! I'll look for it... But the whole point is: this need of a generic cross-tab is really annoying for a large number of people, it has been there for a long time, and I know some people who just walk away from postgreSQL only because this feature is lacking, and they return happily to their m$-access, therefore ignoring the pure wealth of postgreSQL: sad, isn't it?... A+ Pierre -- Pierre Chevalier Mesté Duran 32100 Condom Tél+fax :09 75 27 45 62 05 62 28 06 83 06 37 80 33 64 Émail: pierre.chevalier1967CHEZfree.fr icq# : 10432285 http://pierremariechevalier.free.fr/ Logiciels Libres dans le Gers: http://gnusquetaires.org/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
Pavel Stehule claviota: ... But what I would like to do is to redirect the output of the function (that is, the 'result' cursor) to a view, which will be used in other places. I thought something like FETCH INTO would do the trick, but it doesn't. Also, I need, at some point, to export the output to some CSV file. I usually do a quick bash script as follows: echo COPY (SELECT * FROM dh_litho ORDER BY id, depto) TO stdout WITH CSV HEADER; | psql bdexplo somefile.csv ... hmm ...it cannot work :(. You cannot forward FETCH ALL statement on server side - without programming in C Ach! Too bad... Oh but... I used to program in C, long time ago, on HP-UX... in this case you need small application for reading cursor and transformation to CVS Actually, if the small application was reading cursor, and transforming it to a VIEW, this would solve both problems at once: something like: CREATE VIEW crosstabbed_thing AS (cursor_to_dataset(SELECT do_cross_cursor(...))); And then: echo COPY (SELECT * FROM crosstabbed_thing) TO stdout WITH CSV HEADER; | psql youpi.csv And there we are! What about this plan? The cursor_to_dataset() should be written, in C if I understand well. I have to dig out my old C book, and browse through postgresql APIs, code examples,etc. I guess... A+ Pierre -- Pierre Chevalier Mesté Duran 32100 Condom Tél+fax :09 75 27 45 62 05 62 28 06 83 06 37 80 33 64 Émail: pierre.chevalier1967CHEZfree.fr icq# : 10432285 http://pierremariechevalier.free.fr/ Logiciels Libres dans le Gers: http://gnusquetaires.org/ -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
On Wed, Jan 27, 2010 at 2:14 AM, Pavel Stehule pavel.steh...@gmail.com wrote: hmm ...it cannot work :(. You cannot forward FETCH ALL statement on server side - without programming in C in this case you need small application for reading cursor and transformation to CVS If I'm understanding what you're doing could you write a function to return a set of record then run the cursor inside the function? -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
Hello, Some time ago, it was written here: ... I think there should be a generic way in Postgres to return from an EAV model. Although I have no evidence on that I keep thinking that the db must be more effective at that than the application would be. ... Yes, thanks. The problem with those function is that they all have an AS (columname type,...) part or equivalent. SWK, I fully understand your needs, and your (our) kind of frustration... I am in a similar situation, with an EAV table, and the need to do crosstab queries, without knowing in advance which columns the query should return, and how many columns. This is for chemical analysis results; laboratories store their results in an EAV way, and it is definitely a good choice, for a large number of reasons. On your side, have you found a decent solution? Has anyone got an answer? I am just about to try this one: http://www.ledscripts.com/tech/article/view/5.html http://www.ledscripts.com/tech/article/view/5.ht= But I don't like this style too much: the crosstab approach seems more natural to me. I may be totally wrong. So if there is a crosstab thing working in a generic way, that would be just super! A+ Pierre -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
2010/1/27 Pierre Chevalier pierre.chevalier1...@free.fr: Hello, Some time ago, it was written here: ... I think there should be a generic way in Postgres to return from an EAV model. Although I have no evidence on that I keep thinking that the db must be more effective at that than the application would be. ... Yes, thanks. The problem with those function is that they all have an AS (columname type,...) part or equivalent. SWK, I fully understand your needs, and your (our) kind of frustration... I am in a similar situation, with an EAV table, and the need to do crosstab queries, without knowing in advance which columns the query should return, and how many columns. This is for chemical analysis results; laboratories store their results in an EAV way, and it is definitely a good choice, for a large number of reasons. On your side, have you found a decent solution? Has anyone got an answer? I am just about to try this one: http://www.ledscripts.com/tech/article/view/5.html http://www.ledscripts.com/tech/article/view/5.ht= But I don't like this style too much: the crosstab approach seems more natural to me. I may be totally wrong. So if there is a crosstab thing working in a generic way, that would be just super! you cannot get crosstab via SELECT statement. There is workaround http://okbob.blogspot.com/2008/08/using-cursors-for-generating-cross.html Pavel A+ Pierre -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
Re: [GENERAL] dynamic crosstab
I always hope that somebody might have something similar but
generic - eg. create those columns automatically and just treat them all
as text.
I came up with this amateurish one based on
http://www.ledscripts.com/tech/article/view/5.html.
Maybe someone can use it:
takes
- a select statement
- a name for the resulting view
- the column name of the id
- the column name of the attribute
- the column name of the value
- the aggregate function used
It recreates the view of the given name as a crosstab of the sql specified.
CREATE OR REPLACE FUNCTION public.create_crosstab_view (eavsql_inarg
varchar, resview varchar, rowid varchar, colid varchar, val varchar, agr
varchar) RETURNS pg_catalog.void AS
$body$
DECLARE
casesql varchar;
dynsql varchar;
r record;
BEGIN
dynsql='';
for r in
select * from pg_views where lower(viewname) = lower(resview)
loop
execute 'DROP VIEW ' || resview;
end loop;
casesql='SELECT DISTINCT ' || colid || ' AS v from (' || eavsql_inarg || ')
eav ORDER BY ' || colid;
FOR r IN EXECUTE casesql Loop
dynsql = dynsql || ', ' || agr || '(CASE WHEN ' || colid || '=' || r.v || '
THEN ' || val || ' ELSE NULL END) AS ' || agr || '_' || r.v;
END LOOP;
dynsql = 'CREATE VIEW ' || resview || ' AS SELECT ' || rowid || dynsql || '
from (' || eavsql_inarg || ') eav GROUP BY ' || rowid;
EXECUTE dynsql;
END
$body$
LANGUAGE 'plpgsql' VOLATILE CALLED ON NULL INPUT SECURITY INVOKER;
---(end of broadcast)---
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
Re: [GENERAL] dynamic crosstab
Joe Conway wrote: Erik Jones wrote: See how postgres handles filling the NULLs for you? What you'd really want to do with this would be to define some functions for setting and getting a person's answers to a given question or set of questions so that you could implement some kind of data integrity with regards to question ids and indices into the answers arrays such as in the example above you'd want to prevent an entry at index 7 when there is no entry in the questions table for question_id=7. It occurs to me that it shouldn't be terribly difficult to make an alternate version of crosstab() that returns an array rather than tuples (back when crosstab() was first written, Postgres didn't support NULL array elements). Is this worth considering for 8.4? How about returning generic rows? Is that possible? It would be really neat if you didn't have to specify the return type in the query that invoked the crosstab. I keep wondering if there's a way to pivot (transpose) a result set defined by the standard. -- Alvaro Herrerahttp://www.CommandPrompt.com/ PostgreSQL Replication, Consulting, Custom Development, 24x7 support ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [GENERAL] dynamic crosstab
Alvaro Herrera wrote: Joe Conway wrote: It occurs to me that it shouldn't be terribly difficult to make an alternate version of crosstab() that returns an array rather than tuples (back when crosstab() was first written, Postgres didn't support NULL array elements). Is this worth considering for 8.4? How about returning generic rows? Is that possible? It would be really neat if you didn't have to specify the return type in the query that invoked the crosstab. Yeah, I was thinking about that as well. I'm not sure how difficult it would be. Hopefully I'll be able to find some time to play with it in the next month or so. I keep wondering if there's a way to pivot (transpose) a result set defined by the standard. I've looked at SQL2003 and couldn't find anything, but then again I could have easily missed it. Joe ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [GENERAL] dynamic crosstab
On Tue, Feb 19, 2008 at 11:56:08AM -0300, Alvaro Herrera wrote: Joe Conway wrote: Erik Jones wrote: See how postgres handles filling the NULLs for you? What you'd really want to do with this would be to define some functions for setting and getting a person's answers to a given question or set of questions so that you could implement some kind of data integrity with regards to question ids and indices into the answers arrays such as in the example above you'd want to prevent an entry at index 7 when there is no entry in the questions table for question_id=7. It occurs to me that it shouldn't be terribly difficult to make an alternate version of crosstab() that returns an array rather than tuples (back when crosstab() was first written, Postgres didn't support NULL array elements). Is this worth considering for 8.4? How about returning generic rows? Is that possible? One hack I've used in the past to get those is serializing the rows: XML, YAML and most recently JSON. It would be really neat if you didn't have to specify the return type in the query that invoked the crosstab. It would be handy :) Cheers, David. -- David Fetter [EMAIL PROTECTED] http://fetter.org/ Phone: +1 415 235 3778 AIM: dfetter666 Yahoo!: dfetter Skype: davidfetter XMPP: [EMAIL PROTECTED] Remember to vote! Consider donating to Postgres: http://www.postgresql.org/about/donate ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [GENERAL] dynamic crosstab
It occurs to me that it shouldn't be terribly difficult to make an alternate version of crosstab() that returns an array rather than tuples (back when crosstab() was first written, Postgres didn't support NULL array elements). Is this worth considering for 8.4? How about returning generic rows? Is that possible? One hack I've used in the past to get those is serializing the rows: XML, YAML and most recently JSON. It would be really neat if you didn't have to specify the return type in the query that invoked the crosstab. It would be handy :) +1 What about (for a 2 dim crosstab anyway) take a table and two column names to group by, and return the following results: an 1-d array with the column names, a 1-d with the rownames, and a 2-d array with the cell values; a function to take these three arrays and make csv readable text would be great; also a function to explode the arrays into a table (like an array_accum inverse), but this would take a type or something. Is this what every one means anyway? ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [GENERAL] dynamic crosstab
Joe wrote It occurs to me that it shouldn't be terribly difficult to make an alternate version of crosstab() that returns an array rather than tuples (back when crosstab() was first written, Postgres didn't support NULL array elements). Is this worth considering for 8.4? I think there should be a generic way in Postgres to return from an EAV model. Although I have no evidence on that I keep thinking that the db must be more effective at that than the application would be. I was hoping that now with PG supporting plan invalidation it would be possible to return a recordset. If there is no generic way to return a recordset than being able to return an array is much better than nothing. B. ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [GENERAL] dynamic crosstab
Erik Jones wrote: First, please stop top-posting. It makes it difficult for both me and others to know to whom/what you are replying. Sorry, I don't know much about mailing list customs - I had to look up what top-posting is. I will behave now ... I would prefer to keep the complications for when I retrieve the data rather then when I store it. I could imagine something like this though to create a crosstab as an array, but I am afraid that there is no assurance that the resulting array would contain the values in the same order for each focus: tbl(eID, aID, value) Select eID, array_accum(value) from ( (Select Distinct eID from tbl) e CROSS JOIN (Select Distinct aID from tbl) a ) ea LEFT OUTER JOIN tbl USING (eID, aID) GROUP BY eID B. ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [GENERAL] dynamic crosstab
Balázs Klein wrote: I was hoping that now with PG supporting plan invalidation it would be possible to return a recordset. Plan invalidation has nothing to do with it. In Postgres a returned recordset can be used as a row source in the FROM clause -- this requires data type information to be known at parse time. Joe ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [GENERAL] dynamic crosstab
On Feb 15, 2008, at 6:29 AM, Balázs Klein wrote: Erik Jones wrote: First, please stop top-posting. It makes it difficult for both me and others to know to whom/what you are replying. Sorry, I don't know much about mailing list customs - I had to look up what top-posting is. I will behave now ... It's cool, now you know :) I would prefer to keep the complications for when I retrieve the data rather then when I store it. Really? When do you think users notice performance hits the most? I'd think, given that answers for a questionnaire are stored as a batch, people running reports on will be the ones to notice, i.e. at retrieval time. I could imagine something like this though to create a crosstab as an array, but I am afraid that there is no assurance that the resulting array would contain the values in the same order for each focus: tbl(eID, aID, value) Select eID, array_accum(value) from ( (Select Distinct eID from tbl) e CROSS JOIN (Select Distinct aID from tbl) a ) ea LEFT OUTER JOIN tbl USING (eID, aID) GROUP BY eID That's cool. I still don't see why you're so set on an EAV, but it's your setup. Watch out, though, big questionnaires will turn into queries with an inordinate amount of joins and performance on those will suck. If you just used arrays directly you could pull all of the answers for a given person and/or questionnaire with pretty simple query. Erik Jones DBA | Emma® [EMAIL PROTECTED] 800.595.4401 or 615.292.5888 615.292.0777 (fax) Emma helps organizations everywhere communicate market in style. Visit us online at http://www.myemma.com ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [GENERAL] dynamic crosstab
given that answers for a questionnaire are stored as a batch Not in our setup - for all sorts of reasons (preserving responses on a connection failure or restart, monitoring response latency in real time, creating adaptive/branching questionnaires) we send each response separately. people running reports on will be the ones to notice, i.e. at retrieval time. I am not sure - different responses are aggregated into different attributes in different ways - those properties need to be retrieved during scoring/report generation, so being able to create a join directly on a response is a good thing for me. But report generation - in our case it must be a DTP quality PDF - is such a beast anyway that db times dwarf compared to pdf generation. The problem comes when I need to present the responses themselves in a human-friendly way - as an export or display or report. Do you think there is a way to ensure that the order of the values in the array below is the same for each person? tbl(eID, aID, value) Select eID, array_accum(value) from ( (Select Distinct eID from tbl) e CROSS JOIN (Select Distinct aID from tbl) a ) ea LEFT OUTER JOIN tbl USING (eID, aID) GROUP BY eID Thx for the help. B. ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [GENERAL] dynamic crosstab
On Feb 14, 2008, at 8:19 PM, Joe Conway wrote: Erik Jones wrote: See how postgres handles filling the NULLs for you? What you'd really want to do with this would be to define some functions for setting and getting a person's answers to a given question or set of questions so that you could implement some kind of data integrity with regards to question ids and indices into the answers arrays such as in the example above you'd want to prevent an entry at index 7 when there is no entry in the questions table for question_id=7. It occurs to me that it shouldn't be terribly difficult to make an alternate version of crosstab() that returns an array rather than tuples (back when crosstab() was first written, Postgres didn't support NULL array elements). Is this worth considering for 8.4? That's a great idea. At the very least someone (you? me?) could start work on it and if it doesn't go into the main contrib package it could be made available on pgfoundry. Erik Jones DBA | Emma® [EMAIL PROTECTED] 800.595.4401 or 615.292.5888 615.292.0777 (fax) Emma helps organizations everywhere communicate market in style. Visit us online at http://www.myemma.com ---(end of broadcast)--- TIP 2: Don't 'kill -9' the postmaster
Re: [GENERAL] dynamic crosstab
Balázs Klein wrote: I was hoping that now with PG supporting plan invalidation it would be possible to return a recordset. Plan invalidation has nothing to do with it. In Postgres a returned recordset can be used as a row source in the FROM clause -- this requires data type information to be known at parse time. Joe I thought that it includes that the return type can be changed/redefined at runtime. No luck there than. Thx. B. ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [GENERAL] dynamic crosstab
On Feb 15, 2008, at 9:56 AM, Balázs Klein wrote: given that answers for a questionnaire are stored as a batch Not in our setup - for all sorts of reasons (preserving responses on a connection failure or restart, monitoring response latency in real time, creating adaptive/branching questionnaires) we send each response separately. people running reports on will be the ones to notice, i.e. at retrieval time. I am not sure - different responses are aggregated into different attributes in different ways - those properties need to be retrieved during scoring/report generation, so being able to create a join directly on a response is a good thing for me. But report generation - in our case it must be a DTP quality PDF - is such a beast anyway that db times dwarf compared to pdf generation. The problem comes when I need to present the responses themselves in a human-friendly way - as an export or display or report. Do you think there is a way to ensure that the order of the values in the array below is the same for each person? tbl(eID, aID, value) Select eID, array_accum(value) from ( (Select Distinct eID from tbl) e CROSS JOIN (Select Distinct aID from tbl) a ) ea LEFT OUTER JOIN tbl USING (eID, aID) GROUP BY eID The only way to ever guarantee a particular order is via an ORDER BY clause. Erik Jones DBA | Emma® [EMAIL PROTECTED] 800.595.4401 or 615.292.5888 615.292.0777 (fax) Emma helps organizations everywhere communicate market in style. Visit us online at http://www.myemma.com ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [GENERAL] dynamic crosstab
-Original Message- Do youthink there is a way to ensure that the order of the values in the array below is the same for each person? tbl(eID, aID, value) Select eID, array_accum(value) from ( (Select Distinct eID from tbl) e CROSS JOIN (Select Distinct aID from tbl) a ) ea LEFT OUTER JOIN tbl USING (eID, aID) GROUP BY eID The only way to ever guarantee a particular order is via an ORDER BY clause. Sure. I just didn’t know where to put it - most aggregates don't care about the row order, but for this one it is important. ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org/
Re: [GENERAL] dynamic crosstab
On Fri, Feb 15, 2008 at 9:56 AM, Balázs Klein [EMAIL PROTECTED] wrote: given that answers for a questionnaire are stored as a batch Not in our setup - for all sorts of reasons (preserving responses on a connection failure or restart, monitoring response latency in real time, creating adaptive/branching questionnaires) we send each response separately. people running reports on will be the ones to notice, i.e. at retrieval time. I am not sure - different responses are aggregated into different attributes in different ways - those properties need to be retrieved during scoring/report generation, so being able to create a join directly on a response is a good thing for me. But report generation - in our case it must be a DTP quality PDF - is such a beast anyway that db times dwarf compared to pdf generation. Also, if you need to you can probably add a slony machine to your setup to run the reports on, and it doesn't matter how many reports you run, your production system will only have to run the user interfacing side. This allows for all kinds of optimizing indexing on the reporting server that you might not want to have on the production server. ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [GENERAL] dynamic crosstab
Hi, Yes I know that SPSS can do this - in fact that is the only way I could solve this so far, but that is a very expensive workaround for anybody not currently owning SPSS. Thanks. SWK -Original Message- From: jr [mailto:[EMAIL PROTECTED] Sent: Wednesday, February 13, 2008 1:31 PM To: SunWuKung Subject: Re: dynamic crosstab hi SWK SunWuKung wrote: I know that most db people don't care much about pivot/crosstab in the db but imagine this situation: I am storing questionnaire results on people. Since the questionnaires are created by users I have no other way than using an EAV model like are you using the right tool for this task? Moreover my users can't do anything with this dataformat - they need to pivot it offline anyway, which is not easy (Excel cant do it, Access cant do it, numberGo cant do it for different reasons). back at college we used SPSS - the Statistical Package for Social Sciences. Please let me know if you know of a good db based way to create a dynamic crosstab in Postgres - or why there shouldn't be one. to be honest I don't; I think that a specialised product (such as SPSS) will solve both problems in one stroke. -- regards, jr. ([EMAIL PROTECTED]) ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [GENERAL] dynamic crosstab
Hi, ye, hundreds of columns - but there is no helping it, that’s the way many questionnaire are and the representation of the responses (when not in a database) is always one person per row. I would need this for exporting, but also to show results online. Although it’s a good idea I am afraid that an array could only help me when the info I store about all the persons in the query are exactly the same (there wouldn’t be empty cells in a crosstab) - it’s very useful for some cases but in general that sounds like a dangerous presumption for me. I think this is a generic shortcoming of Postgres - whenever you are forced to create an EAV (Entity-Attribute-Value) model you have no generic or way of going back to the usual one entity per row model. This is something that Access has been able to do (up to 255 columns) as far as I can remember. When I google about this topic I find that the majority of people are still referring to that solution as the easiest for this purpose. Tablefunc crosstab is so close to a good solution for this with the syntax where you could specify the columns with a query - the only shortcoming is that you still have to enumerate the columns and their datatype. I always hope that somebody might have something similar but generic - eg. create those columns automatically and just treat them all as text. Regards, SWK -Original Message- From: Tino Wildenhain [mailto:[EMAIL PROTECTED] Sent: Wednesday, February 13, 2008 2:05 PM To: SunWuKung Cc: pgsql-general@postgresql.org Subject: Re: [GENERAL] dynamic crosstab Hi, SunWuKung wrote: Hi, I found this to create dynamic crosstabs (where the resulting columns ... This could work although for hundreds of columns it looks a bit scary for me. Well I'd say hundreds of columns are always scary, no matter how you do it :-) ... I know that most db people don't care much about pivot/crosstab in the db but imagine this situation: I am storing questionnaire results on people. Since the questionnaires are created by users I have no other way than using an EAV model like personID, questionID, responseValue to store responses. Now this table gets long 300 question per questionnaire, 3000 people and we have 1m row. Now whenever I need to download this data in my case 2/3rd of it would be redundant if I could pivot it first - and in a 20MB csv its significant (I know its a tradeoff between processing and storage). Moreover my users can't do anything with this dataformat - they need to pivot it offline anyway, which is not easy (Excel cant do it, Access cant do it, numberGo cant do it for different reasons). What about not pivoting it? You can run your analysis directly against your database. Although the application could do it I think this is a generic functionality that the database is more suited for. Well after all you want a CSV not a table. You could shortcut this with a generic query which creates array out of your columns and join them to a CSV line. This would just be outputted as one single column from database. Please let me know if you know of a good db based way to create a dynamic crosstab in Postgres - or why there shouldn't be one. See above :-) Regards Tino Internal Virus Database is out-of-date. Checked by AVG Free Edition. Version: 7.5.503 / Virus Database: 269.16.0/1137 - Release Date: 11/18/2007 5:15 PM ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [GENERAL] dynamic crosstab
Yes, once I have the select outputting it to CSV is not a problem. As you say PG handles that nicely. Thx SWK -Original Message- From: Reece Hart [mailto:[EMAIL PROTECTED] Sent: Wednesday, February 13, 2008 9:39 PM To: Tino Wildenhain Cc: SunWuKung; pgsql-general@postgresql.org Subject: Re: [GENERAL] dynamic crosstab On Wed, 2008-02-13 at 14:04 +0100, Tino Wildenhain wrote: Well after all you want a CSV not a table. You could shortcut this with a generic query which creates array out of your columns and join them to a CSV line. This would just be outputted as one single column from database. Depending on your use case, this may be a better way: In psql: = \copy (select col1,col2,col3 from data) TO data.csv CSV HEADER or on the command line: $ psql -c '\copy (select col1,col2,col3 from data) TO data.csv CSV HEADER' Strictly speaking, the CSV formatting isn't being done in the database but rather by psql. -Reece -- Reece Hart, http://harts.net/reece/, GPG:0x25EC91A0 ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [GENERAL] dynamic crosstab
Balázs Klein wrote: Hi, Yes I know that SPSS can do this - in fact that is the only way I could solve this so far, but that is a very expensive workaround for anybody not currently owning SPSS. Huh, perhaps you could try with PSPP ... (I don't know if it can do it, but I know it is supposed to be a replacement to SPSS). -- Alvaro Herrerahttp://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc. ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org/
Re: [GENERAL] dynamic crosstab
On Feb 14, 2008, at 2:04 AM, Balázs Klein wrote: Hi, ye, hundreds of columns - but there is no helping it, that’s the way many questionnaire are and the representation of the responses (when not in a database) is always one person per row. I would need this for exporting, but also to show results online. Although it’s a good idea I am afraid that an array could only help me when the info I store about all the persons in the query are exactly the same (there wouldn’t be empty cells in a crosstab) - it’s very useful for some cases but in general that sounds like a dangerous presumption for me. As of versions = 8.2 you can store NULL values in arrays. Perhaps you could have a Question - Index table and then use an array per person for their answers. I think this is a generic shortcoming of Postgres - whenever you are forced to create an EAV (Entity-Attribute-Value) model you have no generic or way of going back to the usual one entity per row model. This is something that Access has been able to do (up to 255 columns) as far as I can remember. When I google about this topic I find that the majority of people are still referring to that solution as the easiest for this purpose. Tablefunc crosstab is so close to a good solution for this with the syntax where you could specify the columns with a query - the only shortcoming is that you still have to enumerate the columns and their datatype. I always hope that somebody might have something similar but generic - eg. create those columns automatically and just treat them all as text. Have a look at http://www.varlena.com/varlena/GeneralBits/110.php for a totally different approach to questionnaires. Erik Jones DBA | Emma® [EMAIL PROTECTED] 800.595.4401 or 615.292.5888 615.292.0777 (fax) Emma helps organizations everywhere communicate market in style. Visit us online at http://www.myemma.com ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [GENERAL] dynamic crosstab
Hi, the part that I don't know is how to put those NULLs in. It could well be doable I just can't do it myself. How does the query look like that produces from this input: PersonID AttributeID Value 1 1 aaa 1 2 bbb 1 3 ccc 2 1 ddd 2 3 eee this output, without manually enumerating the attributeids: 1 (aaa,bbb,ccc) 2 (ddd,NULL,eee) Thx. B. -Original Message- From: Erik Jones [mailto:[EMAIL PROTECTED] Sent: Thursday, February 14, 2008 5:15 PM To: Balázs Klein Cc: 'Tino Wildenhain'; 'SunWuKung'; pgsql-general@postgresql.org Subject: Re: [GENERAL] dynamic crosstab On Feb 14, 2008, at 2:04 AM, Balázs Klein wrote: Hi, ye, hundreds of columns - but there is no helping it, that’s the way many questionnaire are and the representation of the responses (when not in a database) is always one person per row. I would need this for exporting, but also to show results online. Although it’s a good idea I am afraid that an array could only help me when the info I store about all the persons in the query are exactly the same (there wouldn’t be empty cells in a crosstab) - it’s very useful for some cases but in general that sounds like a dangerous presumption for me. As of versions = 8.2 you can store NULL values in arrays. Perhaps you could have a Question - Index table and then use an array per person for their answers. I think this is a generic shortcoming of Postgres - whenever you are forced to create an EAV (Entity-Attribute-Value) model you have no generic or way of going back to the usual one entity per row model. This is something that Access has been able to do (up to 255 columns) as far as I can remember. When I google about this topic I find that the majority of people are still referring to that solution as the easiest for this purpose. Tablefunc crosstab is so close to a good solution for this with the syntax where you could specify the columns with a query - the only shortcoming is that you still have to enumerate the columns and their datatype. I always hope that somebody might have something similar but generic - eg. create those columns automatically and just treat them all as text. Have a look at http://www.varlena.com/varlena/GeneralBits/110.php for a totally different approach to questionnaires. Erik Jones DBA | Emma® [EMAIL PROTECTED] 800.595.4401 or 615.292.5888 615.292.0777 (fax) Emma helps organizations everywhere communicate market in style. Visit us online at http://www.myemma.com ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
Re: [GENERAL] dynamic crosstab
On Feb 14, 2008, at 10:56 AM, Balázs Klein wrote: -Original Message- From: Erik Jones [mailto:[EMAIL PROTECTED] Sent: Thursday, February 14, 2008 5:15 PM To: Balázs Klein Cc: 'Tino Wildenhain'; 'SunWuKung'; pgsql-general@postgresql.org Subject: Re: [GENERAL] dynamic crosstab On Feb 14, 2008, at 2:04 AM, Balázs Klein wrote: Hi, ye, hundreds of columns - but there is no helping it, that’s the way many questionnaire are and the representation of the responses (when not in a database) is always one person per row. I would need this for exporting, but also to show results online. Although it’s a good idea I am afraid that an array could only help me when the info I store about all the persons in the query are exactly the same (there wouldn’t be empty cells in a crosstab) - it’s very useful for some cases but in general that sounds like a dangerous presumption for me. As of versions = 8.2 you can store NULL values in arrays. Perhaps you could have a Question - Index table and then use an array per person for their answers. I think this is a generic shortcoming of Postgres - whenever you are forced to create an EAV (Entity-Attribute-Value) model you have no generic or way of going back to the usual one entity per row model. This is something that Access has been able to do (up to 255 columns) as far as I can remember. When I google about this topic I find that the majority of people are still referring to that solution as the easiest for this purpose. Tablefunc crosstab is so close to a good solution for this with the syntax where you could specify the columns with a query - the only shortcoming is that you still have to enumerate the columns and their datatype. I always hope that somebody might have something similar but generic - eg. create those columns automatically and just treat them all as text. Have a look at http://www.varlena.com/varlena/GeneralBits/110.php for a totally different approach to questionnaires. Erik Jones Hi, the part that I don't know is how to put those NULLs in. It could well be doable I just can't do it myself. How does the query look like that produces from this input: PersonID AttributeID Value 1 1 aaa 1 2 bbb 1 3 ccc 2 1 ddd 2 3 eee this output, without manually enumerating the attributeids: 1 (aaa,bbb,ccc) 2 (ddd,NULL,eee) Thx. B. My point was to get rid of the the EAV setup. Something like: CREATE TABLE questions ( question_id serial primary key, question text not null ); CREATE TABLE people ( person_id serial primary key, ); CREATE TABLE answers ( person_id integer references people, answers text[] ); where the indexes into answers are ids from questions. You don't get any easy foreign keys for those indexes into the questions table, which you definitely don't have with the EAV setup anyway, but with this you don't need any kind of pivot/crosstab functionality. Erik Jones DBA | Emma® [EMAIL PROTECTED] 800.595.4401 or 615.292.5888 615.292.0777 (fax) Emma helps organizations everywhere communicate market in style. Visit us online at http://www.myemma.com ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [GENERAL] dynamic crosstab
I can't imagine how I could store data directly that way (beside the usual thing that whenever I can I aim to store scalar value in a column). To do what you suggest I could have this: 1 (aaa,bbb,ccc) 2 (ddd,NULL,eee) but for this I would need to store a NULL for a person for all the questions he/she didn't answer. Now answers may come from all sorts of questionnaires so most people will only have responses on a subset, so this does not seem feasible. Or this: 1 (aaa,bbb,ccc) 2 (ddd,eee) but this would be loosing the purpose - there is no longer a meaningful way to compare the same info at different people. So directly storing the info in this structure does not seem to be the way for me. On the other hand a query may be able to generate the proper array without the usual problem of outputting unknown number of columns. thx B. -Original Message- From: Erik Jones [mailto:[EMAIL PROTECTED] Sent: Thursday, February 14, 2008 6:14 PM To: Balázs Klein Cc: 'Tino Wildenhain'; pgsql-general@postgresql.org Subject: Re: [GENERAL] dynamic crosstab On Feb 14, 2008, at 10:56 AM, Balázs Klein wrote: -Original Message- From: Erik Jones [mailto:[EMAIL PROTECTED] Sent: Thursday, February 14, 2008 5:15 PM To: Balázs Klein Cc: 'Tino Wildenhain'; 'SunWuKung'; pgsql-general@postgresql.org Subject: Re: [GENERAL] dynamic crosstab On Feb 14, 2008, at 2:04 AM, Balázs Klein wrote: Hi, ye, hundreds of columns - but there is no helping it, thats the way many questionnaire are and the representation of the responses (when not in a database) is always one person per row. I would need this for exporting, but also to show results online. Although its a good idea I am afraid that an array could only help me when the info I store about all the persons in the query are exactly the same (there wouldnt be empty cells in a crosstab) - its very useful for some cases but in general that sounds like a dangerous presumption for me. As of versions = 8.2 you can store NULL values in arrays. Perhaps you could have a Question - Index table and then use an array per person for their answers. I think this is a generic shortcoming of Postgres - whenever you are forced to create an EAV (Entity-Attribute-Value) model you have no generic or way of going back to the usual one entity per row model. This is something that Access has been able to do (up to 255 columns) as far as I can remember. When I google about this topic I find that the majority of people are still referring to that solution as the easiest for this purpose. Tablefunc crosstab is so close to a good solution for this with the syntax where you could specify the columns with a query - the only shortcoming is that you still have to enumerate the columns and their datatype. I always hope that somebody might have something similar but generic - eg. create those columns automatically and just treat them all as text. Have a look at http://www.varlena.com/varlena/GeneralBits/110.php for a totally different approach to questionnaires. Erik Jones Hi, the part that I don't know is how to put those NULLs in. It could well be doable I just can't do it myself. How does the query look like that produces from this input: PersonID AttributeID Value 1 1 aaa 1 2 bbb 1 3 ccc 2 1 ddd 2 3 eee this output, without manually enumerating the attributeids: 1 (aaa,bbb,ccc) 2 (ddd,NULL,eee) Thx. B. My point was to get rid of the the EAV setup. Something like: CREATE TABLE questions ( question_id serial primary key, question text not null ); CREATE TABLE people ( person_id serial primary key, ); CREATE TABLE answers ( person_id integer references people, answers text[] ); where the indexes into answers are ids from questions. You don't get any easy foreign keys for those indexes into the questions table, which you definitely don't have with the EAV setup anyway, but with this you don't need any kind of pivot/crosstab functionality. Erik Jones DBA | Emma® [EMAIL PROTECTED] 800.595.4401 or 615.292.5888 615.292.0777 (fax) Emma helps organizations everywhere communicate market in style. Visit us online at http://www.myemma.com ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [GENERAL] dynamic crosstab
On Feb 14, 2008, at 3:49 PM, Klein Balazs wrote:
My point was to get rid of the the EAV setup. Something like:
CREATE TABLE questions (
question_id serial primary key,
question text not null
);
CREATE TABLE people (
person_id serial primary key,
);
CREATE TABLE answers (
person_id integer references people,
answers text[]
);
where the indexes into answers are ids from questions. You don't get
any easy foreign keys for those indexes into the questions table,
which you definitely don't have with the EAV setup anyway, but with
this you don't need any kind of pivot/crosstab functionality.
I can't imagine how I could store data directly that way (beside
the usual
thing that whenever I can I aim to store scalar value in a column).
To do what you suggest I could have this:
1 (aaa,bbb,ccc)
2 (ddd,NULL,eee)
but for this I would need to store a NULL for a person for all the
questions
he/she didn't answer. Now answers may come from all sorts of
questionnaires
so most people will only have responses on a subset, so this does
not seem
feasible.
Or this:
1 (aaa,bbb,ccc)
2 (ddd,eee)
but this would be loosing the purpose - there is no longer a
meaningful way
to compare the same info at different people.
So directly storing the info in this structure does not seem to be
the way
for me. On the other hand a query may be able to generate the
proper array
without the usual problem of outputting unknown number of columns.
First, please stop top-posting. It makes it difficult for both me
and others to know to whom/what you are replying.
Now on to the meat of the topic! When using arrays you do not need
to manually store NULLS -- they are implied by gaps in array
indices. Observe:
CREATE TABLE questions (
question_id INTEGER PRIMARY KEY,
question_text TEXT NOT NULL
);
CREATE TABLE people (
person_id SERIAL PRIMARY KEY,
answers TEXT[]
);
INSERT INTO questions (question_id, question_text) VALUES (2, 'Will
arrays work?'), (5, 'Can pigs fly?');
INSERT INTO people (person_id) VALUES (1), (2);
UPDATE people
SET answers[2] = 'yep!',
answers[5] = 'nope!',
answers[7] = 'this shouldn''t be here!'
where person_id=1;
UPDATE people
SET answers[5]='if only they had wings'
where person_id=2;
SELECT * FROM people;
person_id | answers
---
+-
1 | [2:7]={yep!,NULL,NULL,nope!,NULL,this shouldn't
be here!}
2 | [5:5]={if only they had wings}
See how postgres handles filling the NULLs for you? What you'd
really want to do with this would be to define some functions for
setting and getting a person's answers to a given question or set of
questions so that you could implement some kind of data integrity
with regards to question ids and indices into the answers arrays such
as in the example above you'd want to prevent an entry at index 7
when there is no entry in the questions table for question_id=7.
This whole thing is still wide open for adding extra layers such as
question groupings for separate questionnaires, etc.
Erik Jones
DBA | Emma®
[EMAIL PROTECTED]
800.595.4401 or 615.292.5888
615.292.0777 (fax)
Emma helps organizations everywhere communicate market in style.
Visit us online at http://www.myemma.com
---(end of broadcast)---
TIP 5: don't forget to increase your free space map settings
Re: [GENERAL] dynamic crosstab
Erik Jones wrote: See how postgres handles filling the NULLs for you? What you'd really want to do with this would be to define some functions for setting and getting a person's answers to a given question or set of questions so that you could implement some kind of data integrity with regards to question ids and indices into the answers arrays such as in the example above you'd want to prevent an entry at index 7 when there is no entry in the questions table for question_id=7. It occurs to me that it shouldn't be terribly difficult to make an alternate version of crosstab() that returns an array rather than tuples (back when crosstab() was first written, Postgres didn't support NULL array elements). Is this worth considering for 8.4? Joe ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [GENERAL] dynamic crosstab
I found this to create dynamic crosstabs (where the resulting columns are not known beforehand): http://www.ledscripts.com/tech/article/view/5.html (Thanks for Denis Bitouzé on http://www.postgresonline.com/journal/index.php?/archives/14-C rossTab-Queries-in-PostgreSQL-using-tablefunc-contrib.html for pointing it out.). This is basically dynamically generating an SQL string with CASE ... WHEN that will create a view. This could work although for hundreds of columns it looks a bit scary for me. Isn't there a more elegant way to achieve this with tablefunc crosstab and if there isn't don't you think it could/should be there? There is a syntax where you could specify the columns with a SELECT DISTINCT statement - couldn't it also generate the enumeration string eg. presuming that all returning colums are stored as text? Or if that is not possible instead of the enumeration part wouldn't it be better to put a name of the view that could be created/recreated? I know that most db people don't care much about pivot/crosstab in the db but imagine this situation: I am storing questionnaire results on people. Since the questionnaires are created by users I have no other way than using an EAV model like personID, questionID, responseValue to store responses. Now this table gets long 300 question per questionnaire, 3000 people and we have 1m row. Now whenever I need to download this data in my case 2/3rd of it would be redundant if I could pivot it first - and in a 20MB csv its significant (I know its a tradeoff between processing and storage). Moreover my users can't do anything with this dataformat - they need to pivot it offline anyway, which is not easy (Excel cant do it, Access cant do it, numberGo cant do it for different reasons). Although the application could do it I think this is a generic functionality that the database is more suited for. Please let me know if you know of a good db based way to create a dynamic crosstab in Postgres - or why there shouldn't be one. Thanks and regards. SWK Have you tried this crosstab? http://www.postgresql.org/docs/8.3/interactive/tablefunc.html ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [GENERAL] dynamic crosstab
Hi, SunWuKung wrote: Hi, I found this to create dynamic crosstabs (where the resulting columns ... This could work although for hundreds of columns it looks a bit scary for me. Well I'd say hundreds of columns are always scary, no matter how you do it :-) ... I know that most db people don't care much about pivot/crosstab in the db but imagine this situation: I am storing questionnaire results on people. Since the questionnaires are created by users I have no other way than using an EAV model like personID, questionID, responseValue to store responses. Now this table gets long 300 question per questionnaire, 3000 people and we have 1m row. Now whenever I need to download this data in my case 2/3rd of it would be redundant if I could pivot it first - and in a 20MB csv its significant (I know its a tradeoff between processing and storage). Moreover my users can't do anything with this dataformat - they need to pivot it offline anyway, which is not easy (Excel cant do it, Access cant do it, numberGo cant do it for different reasons). What about not pivoting it? You can run your analysis directly against your database. Although the application could do it I think this is a generic functionality that the database is more suited for. Well after all you want a CSV not a table. You could shortcut this with a generic query which creates array out of your columns and join them to a CSV line. This would just be outputted as one single column from database. Please let me know if you know of a good db based way to create a dynamic crosstab in Postgres - or why there shouldn't be one. See above :-) Regards Tino ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org/
Re: [GENERAL] dynamic crosstab
On Wed, 2008-02-13 at 14:04 +0100, Tino Wildenhain wrote: Well after all you want a CSV not a table. You could shortcut this with a generic query which creates array out of your columns and join them to a CSV line. This would just be outputted as one single column from database. Depending on your use case, this may be a better way: In psql: = \copy (select col1,col2,col3 from data) TO data.csv CSV HEADER or on the command line: $ psql -c '\copy (select col1,col2,col3 from data) TO data.csv CSV HEADER' Strictly speaking, the CSV formatting isn't being done in the database but rather by psql. -Reece -- Reece Hart, http://harts.net/reece/, GPG:0x25EC91A0 ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [GENERAL] dynamic crosstab
Yes, thanks. The problem with those function is that they all have an AS (columname type, ...) part or equivalent. -Original Message- From: Masse Jacques [mailto:[EMAIL PROTECTED] Sent: Wednesday, February 13, 2008 10:20 AM To: SunWuKung; pgsql-general@postgresql.org Subject: RE: [GENERAL] dynamic crosstab I found this to create dynamic crosstabs (where the resulting columns are not known beforehand): http://www.ledscripts.com/tech/article/view/5.html (Thanks for Denis Bitouzé on http://www.postgresonline.com/journal/index.php?/archives/14-C rossTab-Queries-in-PostgreSQL-using-tablefunc-contrib.html for pointing it out.). This is basically dynamically generating an SQL string with CASE ... WHEN that will create a view. This could work although for hundreds of columns it looks a bit scary for me. Isn't there a more elegant way to achieve this with tablefunc crosstab and if there isn't don't you think it could/should be there? There is a syntax where you could specify the columns with a SELECT DISTINCT statement - couldn't it also generate the enumeration string eg. presuming that all returning colums are stored as text? Or if that is not possible instead of the enumeration part wouldn't it be better to put a name of the view that could be created/recreated? I know that most db people don't care much about pivot/crosstab in the db but imagine this situation: I am storing questionnaire results on people. Since the questionnaires are created by users I have no other way than using an EAV model like personID, questionID, responseValue to store responses. Now this table gets long 300 question per questionnaire, 3000 people and we have 1m row. Now whenever I need to download this data in my case 2/3rd of it would be redundant if I could pivot it first - and in a 20MB csv its significant (I know its a tradeoff between processing and storage). Moreover my users can't do anything with this dataformat - they need to pivot it offline anyway, which is not easy (Excel cant do it, Access cant do it, numberGo cant do it for different reasons). Although the application could do it I think this is a generic functionality that the database is more suited for. Please let me know if you know of a good db based way to create a dynamic crosstab in Postgres - or why there shouldn't be one. Thanks and regards. SWK Have you tried this crosstab? http://www.postgresql.org/docs/8.3/interactive/tablefunc.html ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org/
[GENERAL] dynamic crosstab
Hi, I found this to create dynamic crosstabs (where the resulting columns are not known beforehand): http://www.ledscripts.com/tech/article/view/5.html (Thanks for Denis Bitouzé on http://www.postgresonline.com/journal/index.php?/archives/14-CrossTab-Queries-in-PostgreSQL-using-tablefunc-contrib.html for pointing it out.). This is basically dynamically generating an SQL string with CASE ... WHEN that will create a view. This could work although for hundreds of columns it looks a bit scary for me. Isn't there a more elegant way to achieve this with tablefunc crosstab and if there isn't don't you think it could/should be there? There is a syntax where you could specify the columns with a SELECT DISTINCT statement - couldn't it also generate the enumeration string eg. presuming that all returning colums are stored as text? Or if that is not possible instead of the enumeration part wouldn't it be better to put a name of the view that could be created/recreated? I know that most db people don't care much about pivot/crosstab in the db but imagine this situation: I am storing questionnaire results on people. Since the questionnaires are created by users I have no other way than using an EAV model like personID, questionID, responseValue to store responses. Now this table gets long 300 question per questionnaire, 3000 people and we have 1m row. Now whenever I need to download this data in my case 2/3rd of it would be redundant if I could pivot it first - and in a 20MB csv its significant (I know its a tradeoff between processing and storage). Moreover my users can't do anything with this dataformat - they need to pivot it offline anyway, which is not easy (Excel cant do it, Access cant do it, numberGo cant do it for different reasons). Although the application could do it I think this is a generic functionality that the database is more suited for. Please let me know if you know of a good db based way to create a dynamic crosstab in Postgres - or why there shouldn't be one. Thanks and regards. SWK ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
