dynamic crosstab

[SunWuKung]

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

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[Masse Jacques]

Post by SunWuKung
I found this to create dynamic crosstabs (where the resulting
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
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

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[Klein Balazs]

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:***@bordeaux.cemagref.fr]
Sent: Wednesday, February 13, 2008 10:20 AM
To: SunWuKung; pgsql-***@postgresql.org
Subject: RE: [GENERAL] dynamic crosstab

Post by SunWuKung
I found this to create dynamic crosstabs (where the resulting
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
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


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[Pierre Chevalier]

Hello,

Post by Balázs Klein
...
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

[Pavel Stehule]

Post by Pierre Chevalier
Hello,

Post by Balázs Klein
...
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?
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

Post by Pierre Chevalier
A+
Pierre
--
http://www.postgresql.org/mailpref/pgsql-general

[Pierre Chevalier]

Hello,

Post by Pavel Stehule
...
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...

Post by Pavel Stehule

SELECT do_cross_cursor('lab_pjcsa_analytecode', 'FROM

lab_ana_results','sample_id',

Post by Pavel Stehule

'FROM lab_ana_results_sel ',
'value_num');
FETCH ALL FROM result WITH CSV HEADER;
) TO stdout WITH CSV HEADER ;" | psql bdexplo

bash: ***@duran:~/fix_bd_amc$: Aucun fichier ou dossier de ce type
***@duran:~$ ERREUR: erreur de syntaxe sur ou près de « ; »
bash: ERREUR: : commande introuvable
bash: » : commande introuvable
***@duran:~$ LIGNE 4 : 'value_num');
bash: Erreur de syntaxe près du symbole inattendu « ) »
***@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-***@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 : [phone]
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/
____________________________________________________________________________

[Pavel Stehule]

Post by Pierre Chevalier
Hello,

Post by Pavel Stehule
...
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.
- 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
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
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

Post by Pierre Chevalier

Post by Pavel Stehule

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: ERREUR: : commande introuvable
bash: » : commande introuvable
bash: Erreur de syntaxe près du symbole inattendu « ) »
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
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  :    [phone]
              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/
____________________________________________________________________________

[Pavel Stehule]

Post by Pavel Stehule

Post by Pierre Chevalier
...
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
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...

Post by Pavel Stehule
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
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

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  :    [phone]
              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/
____________________________________________________________________________

[Pavel Stehule]

Post by Pavel Stehule

...
Actually, if the small application was reading cursor, and transforming it
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... ;-(

Post by Pavel Stehule
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.

Post by Pavel Stehule
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

Post by Pavel Stehule
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  :    [phone]
              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/
____________________________________________________________________________

[Pierre Chevalier]

Post by Pavel Stehule

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.

Post by Pavel Stehule

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... ;)

Post by Pavel Stehule

Post by Pavel Stehule
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 : [phone] - 06 37 80 33 64
http://pierremariechevalier.free.fr/
Logiciels Libres dans le Gers: http://gnusquetaires.org/

[Pavel Stehule]

Post by Pavel Stehule

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.

Post by Pavel Stehule

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... ;)

Post by Pavel Stehule

Post by Pavel Stehule
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 :  [phone]  - 06 37 80 33 64
 http://pierremariechevalier.free.fr/
 Logiciels Libres dans le Gers: http://gnusquetaires.org/

[Pierre Chevalier]

Post by Pavel Stehule

...
Actually, if the small application was reading cursor, and transforming it
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... ;-(

Post by Pavel Stehule
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.

Post by Pavel Stehule
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?

Post by Pavel Stehule
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 : [phone]
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/
____________________________________________________________________________

[Pierre Chevalier]

Post by Pavel Stehule

Post by Pierre Chevalier
...
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
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...

Post by Pavel Stehule
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 : [phone]
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/
____________________________________________________________________________

[Andy Colson]

Post by Pavel Stehule

Post by Pierre Chevalier
...
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
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

[Andy Colson]

Post by Pavel Stehule

Post by Pierre Chevalier
...
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
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
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;

[Joe Conway]

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

[Pierre Chevalier]

Post by Andy Colson
...

be happy to post a little "get you started" code if you wanted.

Hmm, pretty cryptic to my eyes...
Thanks for not writing everything on one line!

Post by Andy Colson
#!/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'};
{
}
$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
--
Pierre Chevalier Mesté Duran 32100 Condom
Tél : [phone] - 06 37 80 33 64
http://pierremariechevalier.free.fr/
Logiciels Libres dans le Gers: http://gnusquetaires.org/

[Andy Colson]

Post by Pierre Chevalier

{
}

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

[Pierre Chevalier]

Post by Andy Colson

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?

Post by Andy Colson
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...

Post by Andy Colson
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 : [phone] - 06 37 80 33 64
http://pierremariechevalier.free.fr/
Logiciels Libres dans le Gers: http://gnusquetaires.org/

[Scott Marlowe]

Post by Pavel Stehule
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?

[Tino Wildenhain]

Hi,

Post by SunWuKung
Hi,
I found this to create dynamic crosstabs (where the resulting columns

...

Post by SunWuKung
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 :-)

...

Post by SunWuKung
I know that most db people don't care much about pivot/crosstab in the
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.

Post by SunWuKung
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.

Post by SunWuKung
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/

[Reece Hart]

Post by Tino Wildenhain
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

[Balázs Klein]

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:***@harts.net]
Sent: Wednesday, February 13, 2008 9:39 PM
To: Tino Wildenhain
Cc: SunWuKung; pgsql-***@postgresql.org
Subject: Re: [GENERAL] dynamic crosstab

Post by Tino Wildenhain
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

[Balázs Klein]

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:***@wildenhain.de]
Sent: Wednesday, February 13, 2008 2:05 PM
To: SunWuKung
Cc: pgsql-***@postgresql.org
Subject: Re: [GENERAL] dynamic crosstab

Hi,

Post by SunWuKung
Hi,
I found this to create dynamic crosstabs (where the resulting columns

...

Post by SunWuKung
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 :-)

...

Post by SunWuKung
I know that most db people don't care much about pivot/crosstab in the
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.

Post by SunWuKung
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.

Post by SunWuKung
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

[Erik Jones]

Post by Balázs Klein
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.

Post by Balázs Klein
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®
***@myemma.com
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

[Balázs Klein]

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:***@myemma.com]
Sent: Thursday, February 14, 2008 5:15 PM
To: Balázs Klein
Cc: 'Tino Wildenhain'; 'SunWuKung'; pgsql-***@postgresql.org
Subject: Re: [GENERAL] dynamic crosstab

Post by Balázs Klein
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.

Post by Balázs Klein
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®
***@myemma.com
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

[Erik Jones]

Post by Klein Balazs
-----Original Message-----
Sent: Thursday, February 14, 2008 5:15 PM
To: Balázs Klein
Subject: Re: [GENERAL] dynamic crosstab

Post by Balázs Klein
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.

Post by Balázs Klein
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.
PersonID AttributeID Value
1 1 aaa
1 2 bbb
1 3 ccc
2 1 ddd
2 3 eee
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®
***@myemma.com
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

[Klein Balazs]

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:***@myemma.com]
Sent: Thursday, February 14, 2008 6:14 PM
To: Balázs Klein
Cc: 'Tino Wildenhain'; pgsql-***@postgresql.org
Subject: Re: [GENERAL] dynamic crosstab

Post by Klein Balazs
-----Original Message-----
Sent: Thursday, February 14, 2008 5:15 PM
To: Balázs Klein
Subject: 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.

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.
PersonID AttributeID Value
1 1 aaa
1 2 bbb
1 3 ccc
2 1 ddd
2 3 eee
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®
***@myemma.com
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




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TIP 3: Have you checked our extensive FAQ?

http://www.postgresql.org/docs/faq

[Erik Jones]

Post by Erik Jones
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.

Post by Klein Balazs
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).
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.
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®
***@myemma.com
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




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[Joe Conway]

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

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TIP 3: Have you checked our extensive FAQ?

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[Balázs Klein]

Post by Joe Conway
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.


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[Joe Conway]

Post by Balázs Klein
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


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TIP 6: explain analyze is your friend

[Balázs Klein]

Post by Joe Conway

Post by Balázs Klein
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.


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TIP 3: Have you checked our extensive FAQ?

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[Erik Jones]

Post by Joe Conway

Post by Erik Jones
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®
***@myemma.com
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




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TIP 2: Don't 'kill -9' the postmaster

[Alvaro Herrera]

Post by Joe Conway

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.

[Joe Conway]

Post by Alvaro Herrera

Post by Joe Conway
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.

Post by Alvaro Herrera
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

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TIP 3: Have you checked our extensive FAQ?

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[David Fetter]

Post by Alvaro Herrera

Post by Joe Conway

Post by Erik Jones
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.

Post by Alvaro Herrera
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 <***@fetter.org> http://fetter.org/
Phone: [phone] AIM: dfetter666 Yahoo!: dfetter
Skype: davidfetter XMPP: ***@gmail.com

Remember to vote!
Consider donating to Postgres: http://www.postgresql.org/about/donate

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match

[Webb Sprague]

Post by David Fetter

Post by Alvaro Herrera

Post by Joe Conway
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?

XML, YAML and most recently JSON.

Post by Alvaro Herrera
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?

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[Balázs Klein]

Post by Erik Jones
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.


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[Erik Jones]

Post by Balázs Klein

Post by Erik Jones
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 :)

Post by Balázs Klein
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.

Post by Balázs Klein
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
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®
***@myemma.com
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




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TIP 3: Have you checked our extensive FAQ?

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[Balázs Klein]

Post by Erik Jones
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.

Post by Erik Jones
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.


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[Erik Jones]

Post by Balázs Klein

Post by Erik Jones
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.

Post by Erik Jones
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®
***@myemma.com
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




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TIP 6: explain analyze is your friend

[Balázs Klein]

Post by Klein Balazs
-----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.


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[Scott Marlowe]

Post by Balázs Klein

Post by Erik Jones
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.

Post by Erik Jones
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.

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[Balázs Klein]

I always hope that somebody might have something similar but

Post by Balázs Klein
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;


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match

[Balázs Klein]

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:***@tailorware.org.uk]
Sent: Wednesday, February 13, 2008 1:31 PM
To: SunWuKung
Subject: Re: dynamic crosstab

hi SWK

Post by SunWuKung
I know that most db people don't care much about pivot/crosstab in the
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?

Post by SunWuKung
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.

Post by SunWuKung
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.

[Alvaro Herrera]

Post by Balázs Klein
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).

[Florent THOMAS]

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

[Joe Conway]

Post by Florent THOMAS
Hello everybody,
I'm trying to find out how to have a dynamic crosstab as in excel,
ireport,etc...
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