Обсуждение: General advice on user functions
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
On 2/21/07, Dan Harris <fbsd@drivefaster.net> wrote: > 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. this could be be done in a view, a function, or a view function combo. you can select multiple counts at once like this: select (select count(*) from foo) as foo, (select count(*) from bar) as bar; but this may not be appropriate in some cases where something complex is going on. you may certainly return multiple columns from a single call using one of two methods: * out parameters (8.1+) * custom type both of which basically return a record instead of a scalar. any function call can be wrapped in a view which can be as simple as create view foo as select * from my_count_proc(); this is especially advised if you want to float input parameters over a table and also filter the inputs via 'where'. merlin
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
>
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>
> http://archives.postgresql.org
--
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Thank you all for your ideas. I appreciate the quick response. -Dan