Re: "Join" on delimeter aggregate query

Hi

You can create an aggregate function to solve this. A friend of mine asked
the same question a while ago, and I created a possible example solution
for him, which I paste here:

CREATE FUNCTION concat(varchar,varchar) RETURNS varchar    AS 'SELECT CASE          $1 WHEN \'\' THEN $2          ELSE
$1|| \',\'|| $2        END AS RESULT;'    LANGUAGE SQL; 

/* DROP AGGREGATE concat(varchar); */

CREATE AGGREGATE concat ( BASETYPE = varchar, SFUNC = concat, STYPE = varchar, INITCOND = ''
);

/* Example code */

DROP TABLE test;
CREATE TABLE test (     a varchar,     b varchar
);

INSERT INTO test VALUES ('A', '1');
INSERT INTO test VALUES ('A', '3');
INSERT INTO test VALUES ('A', '2');
INSERT INTO test VALUES ('B', 'a');
INSERT INTO test VALUES ('C', 'b');
INSERT INTO test VALUES ('C', 'c');

SELECT a, concat(b) FROM (SELECT a,b FROM test ORDER BY a,b) T GROUP BY a;

/*
a | concat
---+---------A | 1,2,3B | aC | b,c

*/

The ORDER BY is included to sort the rows before they are aggregated. I'm
not sure that this guarantees that they actually will be sorted, but maybe
some of the postgresql hackers can confirm/deny this? I guess this isn't
important to you, though.


On Fri, 6 Jun 2003, Michael A Nachbaur wrote:

> Hello everyone,
>
> I've set up PostgreSQL as the authentication / configuration database for my
> mail server (Postfix + Courier-IMAP), and though it works beautifully, I need
> some help on my aliases query.
>
> You see, define aliases in a database table as rows in a column in the form of
> "Source" and "Target".  The problem is that one source address can be
> delivered to multiple targets (e.g. internal mailing list, or a temporary
> forward to another address), but postfix only processes the first record
> returned from an SQL query.
>
> Postfix can deliver to multiple targets, if you separate the targets with
> comas, like so:
>
> Source             Target
> joe@bob.org   address1@bob.org,address2@bob.org,....
>
> What I would like to do, is something like the following (I know I'd need to
> group the query, but you get the idea):
>
> Select DISTINCT(Source), JOIN(Target, ',') FROM Aliases
>
> Is there any way this can be done with Postfix?
>
>

Eivind

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