Re: need help on writing an aggregate function

On Tue, Nov 16, 2004 at 03:21:44PM -0600, Bruno Wolff III wrote:
> On Tue, Nov 16, 2004 at 12:41:45 -0700,
> subhash(at)nmsu(dot)edu wrote:
> > hi,
> > I was writing my own data type, and, I have to write aggregare
> > function like min() and max() for my datatype. I googled for the
> > user defined aggregate functions, but I could not find any
> > examples for the sfunc and ffunc. Can any of you provide me the
> > source/structure in C or SQL for these two functions of min or max
> > or avg etc? for a complex type as given in the examples. Thanks,
> > subhash.
>
> Here is an example I did to do concatenation:

There's an easier way with the tables below and without a new
aggregate. :)

> drop view people_with_email;
> drop table people2email;
> drop table email;
> drop table people;
>
> create table email (
> email_id integer primary key,
> email_address text not null unique
> );
>
> copy email from stdin with delimiter '|';
> 1|scott(at)scottg(dot)tv
> 2|fred(dot)flintstone(at)blah(dot)com
> 3|barney(at)hodown(dot)com
> 4|barney(dot)rubble(at)hey(dot)org
> \.
>
> create table people (
> person_id integer primary key,
> first_name text not null,
> last_name text not null
> );
>
> copy people from stdin with delimiter '|';
> 1|Scott|Goodwin
> 2|Fred|Flintstone
> 3|Barney|Rubble
> \.
>
> create table people2email (
> person_id integer references people (person_id),
> email_id integer references email (email_id)
> );
>
> copy people2email from stdin with delimiter '|';
> 1|1
> 2|2
> 3|3
> 3|4
> \.

CREATE VIEW people_with_email AS
SELECT
a.first_name,
a.last_name,
array_to_string(
ARRAY(
SELECT b.email_address
FROM
email b
JOIN
people2email r
ON (
r.email_id = b.email_id
AND
r.person_id = a.person_id
)
),
', '
) AS "email(s)"
FROM
people a;

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David Fetter david(at)fetter(dot)org http://fetter.org/
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