Обсуждение: Flattening a kind of 'dynamic' table
Good morning,
I have a table that links two tables and I need to flatten one.
(Please, if I'm just not in the good forum for this, tell me. This is
a performance issue for me, but you might consider this as an SQL
question. Feel free to direct me at the good mailling-list.)
design.products ---> design.product_department_time <--- design.departments
This allows us to fixe a given required time by department for a given product.
- Departments are defined by the user
- Products also
- Time is input for a department (0 and NULL are impossible).
Here a normal listing of design.product_department_time:
product_id | department_id | req_time
------------+---------------+----------
906 | A | 3000
906 | C | 3000
906 | D | 1935
907 | A | 1500
907 | C | 1500
907 | D | 4575
924 | A | 6000
924 | C | 1575
I need to JOIN this data with the product listing we have to produce
and multiply the quantity with this time by departments, and all that
in a row. So departments entries become columns.
I did the following (I formated the query to help out):
SELECT
product_id,
sum(CASE WHEN department_id = 'A' THEN req_time END) AS a,
sum(CASE WHEN department_id = 'C' THEN req_time END) AS c,
sum(CASE WHEN department_id = 'D' THEN req_time END) AS d
FROM design.product_department_time
GROUP BY product_id;
product_id | a | c | d
------------+------+------+------
924 | 6000 | 1575 |
907 | 1500 | 1500 | 4575
906 | 3000 | 3000 | 1935
Now in my software I know all the departments, so programatically I
build a query with a CASE for each department (just like the above).
This is nice, this is working, there is less than 10 departements for
now and about 250 jobs actives in the system. So PostgeSQL will not
die. (My example is more simple because this was an hard-coded test
case, but I would create a case entry for each department.)
But I am wondering what is the most efficient way to do what I need?
After that I need to link (LEFT JOIN) this data with the jobs in the
system. Each job has a product_id related to it, so USING (product_id)
and I multiply the time of each department with the quantity there is
to product. So someone can know how much work time there is to do by
departments.
Thanks for any input, comments, tips, help, positive criticism to
learn more, etc.
--
Alexandre Leclerc
Alexandre wrote:
> Here a normal listing of design.product_department_time:
> product_id | department_id | req_time
> ------------+---------------+----------
> 906 | A | 3000
> 906 | C | 3000
> 906 | D | 1935
> 907 | A | 1500
> 907 | C | 1500
> 907 | D | 4575
> 924 | A | 6000
> 924 | C | 1575
> product_id | a | c | d
> ------------+------+------+------
> 924 | 6000 | 1575 |
> 907 | 1500 | 1500 | 4575
> 906 | 3000 | 3000 | 1935
ok, you have a couple of different options here. The first thing that
jumps out at me is to use arrays to cheat using arrays.
Let's start with the normalized result set.
select product_id, department_id, sum(req_time) group by product_id,
department_id
product_id | department_id | sum
924 a 6000
924 c 1575
907 a 1500
[...]
This should be no slower (in fact faster) then your original query and
does not have to be re-coded when you add new departments (you have a
department table, right?).
If you absolutely must have 1 record/product, you can cheat using
arrays:
select q.product_id,
array_accum(q.department_id) as depts,
array_accum(q.req_time) as times
from
(
select product_id, department_id, sum(req_time) as req_time
group by product_id, department_id
) q
group by q.product_id;
select product_id, array_accum(department_id) sum(req_time) group by
product_id
product_id | department_id | sum
924 {a, c} {1500, 1575}
[...]
disclaimer 1: I never checked syntax
disclaimer 2: you may have to add array_accum to pg (check docs)
Merlin
On Thu, 27 Jan 2005 10:23:34 -0500, Alexandre Leclerc
<alexandre.leclerc@gmail.com> wrote:
> Here a normal listing of design.product_department_time:
> product_id | department_id | req_time
> ------------+---------------+----------
> 906 | A | 3000
> 906 | C | 3000
> 906 | D | 1935
> 907 | A | 1500
> 907 | C | 1500
> 907 | D | 4575
> 924 | A | 6000
> 924 | C | 1575
Well, I did something like this recently; it can be done though
maybe not very efficiently...
Unfortunately we will need a rowtype with all the departaments:
CREATE DOMAIN departaments AS (a int, b int, c int, d int, ...);
A function aggregate for this type:
CREATE FUNCTION dep_agg(ds departaments, args text[]) RETURNS departaments AS $$
BEGIN
IF args[1] = 'A' THEN ds.a = args[2]; -- I think it is not
possible to do ds.$args[1] = args[2] equivalent.
ELSIF args[1] = 'B' THEN ds.b = args[2];
ELSIF args[1] = 'C' THEN ds.c = args[2];
ELSIF args[1] = 'D' THEN ds.d = args[2];
END IF;
RETURN ds;
END;
$$ LANUGAGE plpgsql;
THEN an aggregate:
CREATE AGGREGATE dep_aggregate (basetype = text[], stype =
departaments, sfunc =dep_agg);
AND then a view for sugar:
CREATE VIEW prod_dep_time VIEW AS
SELECT product_id, (dep_aggregate(ARRAY[departament_id, req_time]::text[])).*
FROM product_department_time GROUP BY product_id;
And voila. :)
Couple of comments:
-- aggregate takes array[] since making "multicolumn" aggregates is
not possible, as far as I know.
-- I did not check the code, yet I did manage to make it work some time before.
You may need to use "ROWS" or something in the function definition; I
don't remember and can't check it right now.
-- comments welcome. :)
Regards,
Dawid
> Unfortunately we will need a rowtype with all the departaments: > CREATE DOMAIN departaments AS (a int, b int, c int, d int, ...); I think you mean CREATE TYPE departments... Chris
On Thu, 27 Jan 2005 10:44:45 -0500, Merlin Moncure
<merlin.moncure@rcsonline.com> wrote:
> Alexandre wrote:
> > Here a normal listing of design.product_department_time:
> > product_id | department_id | req_time
> > ------------+---------------+----------
> > 906 | A | 3000
> > 906 | C | 3000
> > 906 | D | 1935
> > 907 | A | 1500
> > 907 | C | 1500
> > 907 | D | 4575
> > 924 | A | 6000
> > 924 | C | 1575
> > product_id | a | c | d
> > ------------+------+------+------
> > 924 | 6000 | 1575 |
> > 907 | 1500 | 1500 | 4575
> > 906 | 3000 | 3000 | 1935
>
> ok, you have a couple of different options here. The first thing that
> jumps out at me is to use arrays to cheat using arrays.
> Let's start with the normalized result set.
>
> select product_id, department_id, sum(req_time) group by product_id,
> department_id
>
> product_id | department_id | sum
> 924 a 6000
> 924 c 1575
> 907 a 1500
> [...]
Hello Merlin,
First of all, thanks for your time. Yes this is exactly what I'm doing
right now (if I understand well your point here). All records in
design.product_department_time are unique for each (product_id,
req_time) combo and 0-null values are not possible. This is the first
listing you have.
In my query I added the sum() and GROUP BY stuff to avoid having such a listing:
product_id | a | c | d
------------+------+------+------
906 | 3000 | |
906 | | 3000 |
906 | | | 1935
907 | 1500 | |
907 | | 1500 |
907 | | | 4575
924 | 6000 | |
924 | | 1575 |
So that for a given product_id I have all the times by departments in
a single row (second listing I posted).
> If you absolutely must have 1 record/product, you can cheat using
> arrays:
>
> select q.product_id,
> array_accum(q.department_id) as depts,
> array_accum(q.req_time) as times
> from
> (
> select product_id, department_id, sum(req_time) as req_time
> group by product_id, department_id
> ) q
> group by q.product_id;
>
> select product_id, array_accum(department_id) sum(req_time) group by
> product_id
>
> product_id | department_id | sum
> 924 {a, c} {1500, 1575}
> [...]
I did not used arrays because I didn't think about it, but I don't
know if this is still the most efficient way. My software will have to
work out the data, unless the array expands in good columns. But I'm
not an expert at all. I try to do good DB design, but sometimes this
is more complicated to work with the data.
Here is the table definition if it can help:
design.products (product_id serial PRIMARY KEY, ...);
prod.departments (department_id varchar(3) PRIMARY KEY, ...);
design.product_department_time (
product_id integer REFERENCES design.products ON DELETE
CASCADE ON UPDATE CASCADE,
department_id varchar(3) REFERENCES prod.departments ON DELETE
CASCADE ON UPDATE CASCADE,
req_time integer NOT NULL DEFAULT 0 CHECK (req_time >= 0),
CONSTRAINT product_department_time_pkey PRIMARY KEY (product_id, department_id)
);
And i also have a jobs table which has one product_id attached to one
job with the required quantity to produce. So I must shouw the user
how much time this will require by departments for each jobs. :) This
is a nice report, but I don't want to kill the database each time the
user want to see it.
Thanks for your contrib so far, this will help me looking for other
ways doing it. I'm always ready to hear more!
Regards.
--
Alexandre Leclerc
On Thu, 27 Jan 2005 17:27:40 +0100, Dawid Kuroczko <qnex42@gmail.com> wrote: > On Thu, 27 Jan 2005 10:23:34 -0500, Alexandre Leclerc > <alexandre.leclerc@gmail.com> wrote: > > Here a normal listing of design.product_department_time: > > product_id | department_id | req_time > > ------------+---------------+---------- > > 906 | A | 3000 > > 906 | C | 3000 > > 906 | D | 1935 > > 907 | A | 1500 > > 907 | C | 1500 > > 907 | D | 4575 > > 924 | A | 6000 > > 924 | C | 1575 > > Well, I did something like this recently; it can be done though > maybe not very efficiently... > > Unfortunately we will need a rowtype with all the departaments: > CREATE DOMAIN departaments AS (a int, b int, c int, d int, ...); Thank you for this help Dawid, I'll have to take some time to look at this suggestion. If I must create a domain with all the departments I'll have a problem because the user is creating and deleting departments as it pleases him. Any counter-ideas? Regards. -- Alexandre Leclerc
Alexandre wrote: > On Thu, 27 Jan 2005 10:44:45 -0500, Merlin Moncure > <merlin.moncure@rcsonline.com> wrote: > > Alexandre wrote: > > ok, you have a couple of different options here. The first thing that > > jumps out at me is to use arrays to cheat using arrays. > > Let's start with the normalized result set. > > > > select product_id, department_id, sum(req_time) group by product_id, > > department_id > > > > product_id | department_id | sum > > 924 a 6000 > > 924 c 1575 > > 907 a 1500 > > [...] > > Hello Merlin, > > First of all, thanks for your time. Yes this is exactly what I'm doing > right now (if I understand well your point here). All records in > design.product_department_time are unique for each (product_id, > req_time) combo and 0-null values are not possible. This is the first > listing you have. Right. I expanding departments into columns is basically a dead end. First of all, SQL is not really designed to do this, and second of all (comments continued below) > product_id | a | c | d > ------------+------+------+------ > 906 | 3000 | | > 906 | | 3000 | > 906 | | | 1935 > 907 | 1500 | | > 907 | | 1500 | > 907 | | | 4575 > 924 | 6000 | | > 924 | | 1575 | the above table is more expensive to group than the normalized version above because it is much, much longer. This will get worse and worse as you add more departments. So, whatever you end up doing, I'd advise against expanding rows from a table into columns of a result except for very, very special cases. This is not one of those cases. > I did not used arrays because I didn't think about it, but I don't > know if this is still the most efficient way. My software will have to > work out the data, unless the array expands in good columns. But I'm > not an expert at all. I try to do good DB design, but sometimes this > is more complicated to work with the data. Arrays are a quick'n'dirty way to de-normalize a result set. According to me, de-normalization is o.k. for result sets *only*. Generally, it is inappropriate to de-normalize any persistent object in the database, such as a view (or especially) a table. de-normalizing sets can sometimes simplify client-side coding issues or provide a performance benefit at the query stage (or slow it down, so be careful!) > And i also have a jobs table which has one product_id attached to one > job with the required quantity to produce. So I must shouw the user > how much time this will require by departments for each jobs. :) This > is a nice report, but I don't want to kill the database each time the > user want to see it. You always have the option to do this in code. This basically means ordering the result set and writing a nested loop to pass over the data. If you happen to be using a report engine (and it sounds like you are), some engines can simplify this via a grouping criteria, some can't. If parsing an array string is a pain I happen to have a C++ class handy that can compose/decompose a postgresql array string if: a: no more than 1 dimension and b: array bounds are known Let me know if you need it and I'll send it over. Merlin
On Thu, 27 Jan 2005 13:02:48 -0500, Merlin Moncure
<merlin.moncure@rcsonline.com> wrote:
> Alexandre wrote:
> > On Thu, 27 Jan 2005 10:44:45 -0500, Merlin Moncure
> > <merlin.moncure@rcsonline.com> wrote:
> > > Alexandre wrote:
> > > Let's start with the normalized result set.
> > >
> > > product_id | department_id | sum
> > > 924 a 6000
> > > 924 c 1575
> > > 907 a 1500
> > > [...]
> >
> Right. I expanding departments into columns is basically a dead end.
> First of all, SQL is not really designed to do this, and second of all
> (comments continued below)
Ok, I got it. The basic message is to avoid making columns out of rows
like I'm doing right now, that "de-normalizing" in an array is the way
to go. So I should query and get the results in an array then after my
application will parse the array into the good columns. (I'm
developping a software.)
If I still got it wrong, this is because the 'geek' section of my
brain is in vacation: leave a message and when it'll come back, it'll
explain all this to me! :)
So I found the array_accum function in the doc, so I did create it.
CREATE AGGREGATE array_accum (
sfunc = array_append,
basetype = anyelement,
stype = anyarray,
initcond = '{}'
);
Then I created this new select:
SELECT
product_id,
array_accum(department_id) as a_department_id,
array_accum(req_time) as a_req_time
FROM (SELECT * FROM design.product_department_time) AS tmp
GROUP BY product_id;
It gives:
product_id | a_department_id | a_req_time
------------+-----------------+------------------
924 | {A,C} | {6000,1575}
907 | {A,C,D} | {1500,1500,4575}
906 | {A,C,D} | {3000,3000,1935}
So, the performance should be much better using this agregate approach?
No I thing I'll merge the results in my software, unless you think
that at this point doing a LEFT JOIN with my jobs table is the way to
go, beacuse the performance will be good. (Personally I don't know the
answer of this one.)
> If parsing an array string is a pain I happen to have a C++ class handy
> that can compose/decompose a postgresql array string if:
> a: no more than 1 dimension and
> b: array bounds are known
>
> Let me know if you need it and I'll send it over.
Thank you for your offer. I think parsing an array is the easiest
thing to do for me in all this. :) If I encounter any problem, I'll
drop you a mail.
Regards.
--
Alexandre Leclerc
Alexandre wrote: > > > > > Right. I expanding departments into columns is basically a dead end. > > First of all, SQL is not really designed to do this, and second of all > > (comments continued below) > > Ok, I got it. The basic message is to avoid making columns out of rows yes. This is wrong. > like I'm doing right now, that "de-normalizing" in an array is the way > to go. Only sometimes. Looping application code is another tactic. There may be other things to do as well that don't involve arrays or application code. Consider arrays a (very postgresql specific) tool in your expanding toolchest. De-normalization is a loaded term because we are only presenting queried data in an alternate format (normalization normally applying to data structured within the database). There are many people on this list who will tell you not to de-normalize anything, ever (and most of the time, you shouldn't!). Merlin
On Thu, 27 Jan 2005 16:05:09 -0500, Merlin Moncure <merlin.moncure@rcsonline.com> wrote: > Alexandre wrote: > > like I'm doing right now, that "de-normalizing" in an array is the way > > to go. > > Only sometimes. Looping application code is another tactic. There may > be other things to do as well that don't involve arrays or application > code. Consider arrays a (very postgresql specific) tool in your > expanding toolchest. I take good notes of that. All this opened to me other ways for solutions, so I'm glad of that. I'll take more time to think about all that. > De-normalization is a loaded term because we are only presenting queried > data in an alternate format (normalization normally applying to data > structured within the database). There are many people on this list who > will tell you not to de-normalize anything, ever (and most of the time, > you shouldn't!). Thank you for all you help and time for this. Best regards. -- Alexandre Leclerc
On Thu, 27 Jan 2005 12:43:56 -0500, Alexandre Leclerc
<alexandre.leclerc@gmail.com> wrote:
> On Thu, 27 Jan 2005 17:27:40 +0100, Dawid Kuroczko <qnex42@gmail.com> wrote:
> > On Thu, 27 Jan 2005 10:23:34 -0500, Alexandre Leclerc
> > <alexandre.leclerc@gmail.com> wrote:
> > > Here a normal listing of design.product_department_time:
> > > product_id | department_id | req_time
> > > ------------+---------------+----------
> > > 906 | A | 3000
> > > 906 | C | 3000
> > > 906 | D | 1935
> > > 907 | A | 1500
> > > 907 | C | 1500
> > > 907 | D | 4575
> > > 924 | A | 6000
> > > 924 | C | 1575
> >
> > Well, I did something like this recently; it can be done though
> > maybe not very efficiently...
> >
> > Unfortunately we will need a rowtype with all the departaments:
> > CREATE DOMAIN departaments AS (a int, b int, c int, d int, ...);
> Thank you for this help Dawid, I'll have to take some time to look at
> this suggestion. If I must create a domain with all the departments
> I'll have a problem because the user is creating and deleting
> departments as it pleases him.
>
> Any counter-ideas?
I have exactly the same problem with my proposal [1]
I just wish there would be some "native" rows-to-columns
aggregate.
The other approach I used was something like this:
SELECT product_id, a, b, c FROM
(SELECT product_id, a FROM pdt) AS a FULL OUTER JOIN USING(product_id)
(SELECT product_id, b FROM pdt) AS b FULL OUTER JOIN USING(product_id)
(SELECT product_id, c FROM pdt) AS c;
...or similar (I'm typing from memory ;)). Anyway it was good for getting
whole table, but performance well, wasn't the gratest. ;)).
Regards,
Dawid
[1]: I was thinking about a trigger on a "departaments" table,
and then recreating the aggregate and view as needed, but
it isn't the kind of dynamic I had in mind. ;)
On Fri, 28 Jan 2005 09:07:59 +0100, Dawid Kuroczko <qnex42@gmail.com> wrote: > On Thu, 27 Jan 2005 12:43:56 -0500, Alexandre Leclerc > <alexandre.leclerc@gmail.com> wrote: > > On Thu, 27 Jan 2005 17:27:40 +0100, Dawid Kuroczko <qnex42@gmail.com> wrote: > > > On Thu, 27 Jan 2005 10:23:34 -0500, Alexandre Leclerc > > > <alexandre.leclerc@gmail.com> wrote: > > > > Here a normal listing of design.product_department_time: > > > > product_id | department_id | req_time > > > > ------------+---------------+---------- > > > > 906 | A | 3000 > > > > 906 | C | 3000 > > > > 906 | D | 1935 > > > > 907 | A | 1500 > > > > 907 | C | 1500 > > > > 907 | D | 4575 > > > > 924 | A | 6000 > > > > 924 | C | 1575 > > > > > > Well, I did something like this recently; it can be done though > > > maybe not very efficiently... > > > > > > Unfortunately we will need a rowtype with all the departaments: > > > CREATE DOMAIN departaments AS (a int, b int, c int, d int, ...); > > Thank you for this help Dawid, I'll have to take some time to look at > > this suggestion. If I must create a domain with all the departments > > I'll have a problem because the user is creating and deleting > > departments as it pleases him. > > > > Any counter-ideas? > > I have exactly the same problem with my proposal [1] > I just wish there would be some "native" rows-to-columns > aggregate. > > [1]: I was thinking about a trigger on a "departaments" table, > and then recreating the aggregate and view as needed, but > it isn't the kind of dynamic I had in mind. ;) Yep, this is the only thing I also tought: a trigger to add / remove columns when the user add or remove a department... but this is not exactly what I wanted (this is not a very nice db design, from my perspective). Thank you for you help. -- Alexandre Leclerc
Alexandre Leclerc wrote:
>>>>>Here a normal listing of design.product_department_time:
>>>>> product_id | department_id | req_time
>>>>>------------+---------------+----------
>>>>> 906 | A | 3000
>>>>> 906 | C | 3000
>>>>> 906 | D | 1935
>>>>> 907 | A | 1500
>>>>> 907 | C | 1500
>>>>> 907 | D | 4575
>>>>> 924 | A | 6000
>>>>> 924 | C | 1575
Sorry for jumping in on this thread so late -- I haven't been able to
keep up with the lists lately.
If I understand what you want correctly, you should be able to use
crosstab from contrib/tablefunc:
create table product_department_time(product_id int, department_id text,
req_time int);
insert into product_department_time values(906, 'A', 3000);
insert into product_department_time values(906, 'C', 3000);
insert into product_department_time values(906, 'D', 1935);
insert into product_department_time values(907, 'A', 1500);
insert into product_department_time values(907, 'C', 1500);
insert into product_department_time values(907, 'D', 4575);
insert into product_department_time values(924, 'A', 6000);
insert into product_department_time values(924, 'C', 1575);
select * from crosstab(
'select product_id, department_id, req_time
from product_department_time order by 1',
'select ''A'' union all select ''C'' union all select ''D'''
) as (product_id int, a int, c int, d int);
product_id | a | c | d
------------+------+------+------
906 | 3000 | 3000 | 1935
907 | 1500 | 1500 | 4575
924 | 6000 | 1575 |
(3 rows)
You could make this dynamic for new values of department_id by wrapping
it with a PL/pgSQL function.
HTH,
Joe
On Fri, 28 Jan 2005 08:34:27 -0800, Joe Conway <mail@joeconway.com> wrote: > Alexandre Leclerc wrote: > >>>>>Here a normal listing of design.product_department_time: > >>>>> product_id | department_id | req_time > >>>>>------------+---------------+---------- > >>>>> 906 | A | 3000 > >>>>> 906 | C | 3000 > >>>>> 906 | D | 1935 > >>>>> 907 | A | 1500 > >>>>> 907 | C | 1500 > >>>>> 907 | D | 4575 > >>>>> 924 | A | 6000 > >>>>> 924 | C | 1575 > > Sorry for jumping in on this thread so late -- I haven't been able to > keep up with the lists lately. > > If I understand what you want correctly, you should be able to use > crosstab from contrib/tablefunc: I'm a little bit confused on how to install this contirb. I know my contrib package is installed, but I don't know how to make it work in postgresql. (Using 7.4.5-1mdk on Mandrake Linux.) -- Alexandre Leclerc
Alexandre Leclerc wrote: > I'm a little bit confused on how to install this contirb. I know my > contrib package is installed, but I don't know how to make it work in > postgresql. (Using 7.4.5-1mdk on Mandrake Linux.) > Find the file tablefunc.sql and redirect it into your database, e.g. psql mydatabase < /path/to/contrib/scripts/tablefunc.sql I have no idea where that would be on Mandrake, but you could probably do: locate tablefunc.sql On Fedora Core 1 I find it here: /usr/share/pgsql/contrib/tablefunc.sql Also find and read README.tablefunc. HTH, Joe
On Fri, 28 Jan 2005 10:24:37 -0800, Joe Conway <mail@joeconway.com> wrote: > Alexandre Leclerc wrote: > > I'm a little bit confused on how to install this contirb. I know my > > contrib package is installed, but I don't know how to make it work in > > postgresql. (Using 7.4.5-1mdk on Mandrake Linux.) > > > locate tablefunc.sql Thank you. The RPM was not installing, but I manage to extract it's contact and grap the .sql file in the contrib. So I installed the function manually. Now it's time to evaluate performance of this! Thanks for your help! -- Alexandre Leclerc
On Fri, 28 Jan 2005 10:24:37 -0800, Joe Conway <mail@joeconway.com> wrote:
> Alexandre Leclerc wrote:
> > I'm a little bit confused on how to install this contirb. I know my
> > contrib package is installed, but I don't know how to make it work in
> > postgresql. (Using 7.4.5-1mdk on Mandrake Linux.)
> >
>
> Find the file tablefunc.sql and redirect it into your database, e.g.
>
> psql mydatabase < /path/to/contrib/scripts/tablefunc.sql
>
> I have no idea where that would be on Mandrake, but you could probably do:
>
> locate tablefunc.sql
>
> On Fedora Core 1 I find it here:
> /usr/share/pgsql/contrib/tablefunc.sql
>
> Also find and read README.tablefunc.
>
> HTH,
WHOA! Yess! Exactly the thing! Amazing! :)))
Regards,
Dawid
> Alexandre Leclerc wrote: > Sorry for jumping in on this thread so late -- I haven't been able to > select * from crosstab( > 'select product_id, department_id, req_time > from product_department_time order by 1', > 'select ''A'' union all select ''C'' union all select ''D''' > ) as (product_id int, a int, c int, d int); I forgot you could do this...This would certainly be easier than parsing array values returned from array_accum. It will probably be faster as well...but with the array approach the query would not have to be modified each time a new department was added. That said, a crosstab based query could be built easily enough from a department query on the client and then you have the best of both worlds. Merlin
On Fri, 4 Feb 2005 12:48:43 -0500, Merlin Moncure <merlin.moncure@rcsonline.com> wrote: > > Alexandre Leclerc wrote: > > Sorry for jumping in on this thread so late -- I haven't been able to > > select * from crosstab( > > 'select product_id, department_id, req_time > > from product_department_time order by 1', > > 'select ''A'' union all select ''C'' union all select ''D''' > > ) as (product_id int, a int, c int, d int); > > I forgot you could do this...This would certainly be easier than parsing > array values returned from array_accum. It will probably be faster as > well...but with the array approach the query would not have to be > modified each time a new department was added. That said, a crosstab > based query could be built easily enough from a department query on the > client and then you have the best of both worlds. Hello Merlin, Well, I'm glad because with all this i've learn a lot of new things. Finally, the crosstab solution is very fast and is simple for me to use. I get my super-bug-jumbo-dbkiller-query run in about 210ms (seeking many tables and so). I had a score of 2480ms before. (This is a much more complex query; the cross table thing had to be included in this one.) This is much better! :) In all, thanks for your help. Regards. -- Alexandre Leclerc