Multiple Parameters to an Aggregate Function

From: "Anthony Bouvier" <anthony(at)developware(dot)com>
To: <pgsql-sql(at)postgresql(dot)org>
Subject: Multiple Parameters to an Aggregate Function
Date: 2001-10-16 18:23:43
Message-ID: CBEBKIKGCCOCPDEMKBBJMEBCCAAA.anthony@developware.com
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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

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