Re: SQL query - single text value from group by

On Wed, 2004-09-08 at 17:13 +0100, Richard Huxton wrote:
> mike wrote:
> > Hi
> >
> > I am trying to work out if this is possible in a select query
> >
> > I have a group by query which could result in several rows, what I want
> > to do is do a text equivalent of a sum() eg:
> >
> > SELECT sum(inv_id),date,cust
> > from invoice
> > group by date,cust
> >
> > Is there any way to get to a single concatenated inv_id field with just
> > one row?
>
> Yes, you can define your own aggregate. For example, I did this the
> other day:
>
> /*
>    Custom aggregate
>      This aggregate is so we can aggregate text into paragraph blocks
> */
> CREATE OR REPLACE FUNCTION join_paras(text, text) RETURNS text AS
> '
>      SELECT CASE
>          WHEN ($1 = '''') THEN $2
>          ELSE $1 || ''\n'' || $2
>      END;
> ' LANGUAGE 'SQL' IMMUTABLE;
>
> CREATE AGGREGATE agg_paras (sfunc1=join_paras, basetype=text,
> stype1=text, initcond1='');
>
> Note I defined my own text-concatenation function because I wanted to
> insert newlines between each block of text. If you just wanted joined
> text you could use the built-in textcat()
>
> Full specs of create aggregate are in the manuals.
>
> HTH


thanks - as sods law dictates I found a solution just after I posted
along the same lines, after a couple of hours of fruitless googling.