Thread: Multiple Parameters to an Aggregate Function

I have a sub in a Perl script that loops execution the following
statement:
 SELECT url,name FROM links

And formats it like so:
 <a href='$url'>$name</a><br>

A variable ($link_list) is in the loop, holding the concatenated last
statement with the new one.

I would rather do this with FUNCTIONS (and/or AGGREGATES).

So, I CREATEd a FUNCTION:

CREATE FUNCTION format_link(text,text)
RETURNS text AS ' return qq[<a href="http://www.domain.com/$_[0]"
class="body_link">$_[1]</a>];
' LANGUAGE 'plperl';

So in my Perl script, the SQL statement becomes:
 SELECT format_link(url,name) FROM links

However, I still have to loop with Perl -- it would be nice to use an
AGGREGATE to do some of this for me.

I can create an AGGREGATE but from what I can tell, the format of the
sfunc can only have two parameters like so:

sfunc_name(type,type)

Where the first parameter is what was passed before, and the second
parameter is the 'new' info to do stuff to.  Is it not possible to do
something similar to?:

sfunc_name(type,type,type)

So that I can pass the url and name to the AGGREGATE (so it can in turn
pass it to the sfunc)?  Where the sfunc could be something like so:

CREATE FUNCTION link_agg (text,text,text)
RETURNS text AS ' return $_[0] . qq[<a href="http://www.domain.com/$_[0]"
class="body_link">$_[1]</a><br>];
' LANGUAGE 'plperl';

Because then I gain benefit of a stored procedure and cut the SQL in the
script down to:
 SELECT link_agg(url,name) FROM link;

Which will return the entire list at once, instead of needing the script
to loop through multiple fetches.

...

Of course, I may be going about this in an entirely incorrect manner.
Telling me so, with a bit of direction, would also be greatly
appreciated.

BTW:  I tried searching the archives, but there is a database error
("PQconnectPoll() -- connect() failed: Connection refused Is the
postmaster running (with -i) at 'db.hub.org' and accepting connections
on TCP/IP port 5439?"), just so someone knows.

Thanks In Advance,

Anthony Bouvier

On Tue, 16 Oct 2001, Anthony Bouvier wrote:

> I can create an AGGREGATE but from what I can tell, the format of the
> sfunc can only have two parameters like so:
>
> sfunc_name(type,type)
>
> Where the first parameter is what was passed before, and the second
> parameter is the 'new' info to do stuff to.  Is it not possible to do
> something similar to?:
>
> sfunc_name(type,type,type)
>
> So that I can pass the url and name to the AGGREGATE (so it can in turn
> pass it to the sfunc)?  Where the sfunc could be something like so:
>
> CREATE FUNCTION link_agg (text,text,text)
> RETURNS text AS '
>   return $_[0] . qq[<a href="http://www.domain.com/$_[0]"
> class="body_link">$_[1]</a><br>];
> ' LANGUAGE 'plperl';
>
> Because then I gain benefit of a stored procedure and cut the SQL in the
> script down to:
>
>   SELECT link_agg(url,name) FROM link;
>
> Which will return the entire list at once, instead of needing the script
> to loop through multiple fetches.

I have a techdoc about using aggregate functions to create faster
web looping at
 http://www.zope.org/Members/pupq/pg_in_aggregates

It was written w/examples in DTML, Zope's scripting language, rather than
in Perl/DBI, but you should be able to easily follow it.

Essentially, what you want to end up with is something like this:

SELECT make_into_li ( make_into_text ( url, name ) );

where make_into_text is the aggregate, and make_into_text is the
formatting function.

-- 

Joel BURTON  |  joel@joelburton.com  |  joelburton.com  |  aim: wjoelburton
Independent Knowledge Management Consultant