Re: General advice on user functions - Mailing list pgsql-performance

Hi Dan,
    you may take a look at the crosstab contrib module. There you can find a
function that can convert your rows into columns. However, you can also use
the manual approach, as crosstab has its limitations too.
    You can create a TYPE that has all the columns you need, you create a
function that fills and returns this newly created TYPE. Of course the type
will have all those 50 fields defined, so it's boring, but should work. (Take
a look at
http://www.postgresql.org/docs/8.2/interactive/sql-createtype.html).

A Dimecres 21 Febrer 2007 19:33, Dan Harris va escriure:
> I have a new task of automating the export of a very complex Crystal
> Report.  One thing I have learned in the last 36 hours is that the
> export process to PDF is really, really, slooww..
>
> Anyway, that is none of your concern.  But, I am thinking that I can
> somehow utilize some of PG's strengths to work around the bottleneck in
> Crystal.  The main problem seems to be that tens of thousands of rows of
> data must be summarized in the report and calculations made.  Based on
> my recent experience, I'd say that this task would be better suited to
> PG than relying on Crystal Reports to do the summarizing.
>
> The difficulty I'm having is that the data needed is from about 50
> different "snapshots" of counts over time.  The queries are very simple,
> however I believe I am going to need to combine all of these queries
> into a single function that runs all 50 and then returns just the
> count(*) of each as a separate "column" in a single row.
>
> I have been Googling for hours and reading about PL/pgsql functions in
> the PG docs and I have yet to find examples that returns multiple items
> in a single row.  I have seen cases that return "sets of", but that
> appears to be returning multiple rows, not columns.  Maybe this I'm
> barking up the wrong tree?
>
> Here's the gist of what I need to do:
>
> 1) query count of rows that occurred between 14 months ago and 12 months
> ago for a given criteria, then count the rows that occurred between 2
> months ago and current.  Repeat for 50 different where clauses.
>
> 2) return each count(*) as a "column" so that in the end I can say:
>
> select count_everything( ending_date );
>
> and have it return to me:
>
> count_a_lastyear   count_a_last60    count_b_lastyear    count_b_last60
> ----------------   --------------    ----------------    --------------
>   100                150               200                 250
>
> I'm not even sure if a function is what I'm after, maybe this can be
> done in a view?  I am embarrassed to ask something that seems like it
> should be easy, but some key piece of knowledge is escaping me on this.
>
> I don't expect someone to write this for me, I just need a nudge in the
> right direction and maybe a URL or two to get me started.
>
> Thank you for reading this far.
>
> -Dan
>
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Have you searched our list archives?
>
>                http://archives.postgresql.org

--
Albert Cervera Areny
Dept. Informàtica Sedifa, S.L.

Av. Can Bordoll, 149
08202 - Sabadell (Barcelona)
Tel. 93 715 51 11
Fax. 93 715 51 12

====================================================================
........................  AVISO LEGAL  ............................
La   presente  comunicación  y sus anexos tiene como destinatario la
persona a  la  que  va  dirigida, por  lo  que  si  usted lo  recibe
por error  debe  notificarlo  al  remitente  y   eliminarlo   de  su
sistema,  no  pudiendo  utilizarlo,  total  o   parcialmente,   para
ningún  fin.  Su  contenido  puede  tener información confidencial o
protegida legalmente   y   únicamente   expresa  la  opinión     del
remitente.  El   uso   del   correo   electrónico   vía Internet  no
permite   asegurar    ni  la   confidencialidad   de   los  mensajes
ni    su    correcta     recepción.   En    el  caso   de   que   el
destinatario no consintiera la utilización  del correo  electrónico,
deberá ponerlo en nuestro conocimiento inmediatamente.
====================================================================
........................... DISCLAIMER .............................
This message and its  attachments are  intended  exclusively for the
named addressee. If you  receive  this  message  in   error,  please
immediately delete it from  your  system  and notify the sender. You
may  not  use  this message  or  any  part  of it  for any  purpose.
The   message   may  contain  information  that  is  confidential or
protected  by  law,  and  any  opinions  expressed  are those of the
individual    sender.  Internet  e-mail   guarantees   neither   the
confidentiality   nor  the  proper  receipt  of  the  message  sent.
If  the  addressee  of  this  message  does  not  consent to the use
of   internet    e-mail,    please    inform     us    inmmediately.
====================================================================