Re: Merging multiple values into comma-delimited list in a view - Mailing list pgsql-novice

On Wed, Mar 03, 2004 at 15:25:18 -0500,
  Scott Goodwin <scott@scottg.net> wrote:
> Need some help with the following example. I have email, people and
> people2email tables. The people2email table is a one-to-many with one
> person able to have many email addresses, and the people_with_email
> view ties it all together for me. Here's the output when I do a "select
> * from people_with_email;"
>
>  first_name | last_name  |      email_address
> ------------+------------+--------------------------
>  Scott      | Goodwin    | scott@scottg.tv
>  Fred       | Flintstone | fred.flintstone@blah.com
>  Barney     | Rubble     | barney@hodown.com
>  Barney     | Rubble     | barney.rubble@hey.org
>
> What I really want is one person per row, with the email addresses
> concat'd together with commas, like this:

You can write a custom aggregate to do that. A sample function to do this
(concatenate strings) has been posted to at least one of the lists previously
and should be in the archives.

>
> first_name | last_name  |      email_address
> ------------+------------+--------------------------
>  Scott      | Goodwin    | scott@scottg.tv
>  Fred       | Flintstone | fred.flintstone@blah.com
>  Barney     | Rubble     | barney@hodown.com, barney.rubble@hey.org
>
> My question is: how do I modify the select statement that generates the
> people_with_email view so that it generates the output I want?
>
> I'll gladly tie myself to any PG-specific feature that does the job as
> I'll not be moving to any other database software within my lifetime if
> I can help it (and I can:). I wouldn't mind using arrays, but can't
> really change the data type of a column in a view (is there a way to
> CAST it?). Might be able to use a materialized view, which could then
> support array columns, but I'd be satisfied with a plain text string
> that I can split on with Tcl.
>
> The datamodel, with the view and dummy data is below.
>
> thanks,
>
> /s.
>
> ======== data model =========
>
> drop view  people_with_email;
> drop table people2email;
> drop table email;
> drop table people;
>
> create table email (
>    email_id        integer primary key,
>    email_address   varchar(128) not null unique
> );
>
> copy email from stdin with delimiter '|';
> 1|scott@scottg.tv
> 2|fred.flintstone@blah.com
> 3|barney@hodown.com
> 4|barney.rubble@hey.org
> \.
>
> create table people (
>    person_id       integer primary key,
>    first_name      varchar(32) not null,
>    last_name       varchar(32) 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,
>       b.email_address
>   from
>       people a
>   inner join
>       people2email r
>       on
>       a.person_id = r.person_id
>   inner join
>       email b
>       on
>       b.email_id = r.email_id
>       ;
>
>
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