On 03/02/2016 12:18, arnaud gaboury wrote:
> $ psql -V
> psql (PostgreSQL) 9.4.5
>
> I am quite a newbie in psql. I am setting an email server and need to
> create then query psql tables to get some information: mainly email
> address and mail directory.
>
> For now I have created two tables this way. Both tables are in same
> database and schema. I only insert one row in each.
>
> 1- the first one is just a list of all my domains.
>
> -----------------------------------------
> CREATE TABLE email.domain (
> id SERIAL,
> domain TEXT NOT NULL,
> PRIMARY KEY (id)
> );
> ---------------------------------
>
> 2- second is a list of users
>
> --------------------------------------------------
> CREATE TABLE email.mailusers (
> id SERIAL PRIMARY KEY,
> domain_id INTEGER DEFAULT 1, <<-- This ref to email.domain id=1
> password TEXT NOT NULL,
> username TEXT UNIQUE NOT NULL,
> created TIMESTAMP WITH TIME ZONE DEFAULT now();
> ------------------------------------
>
> 3- Then I added a constraint:
>
> ---------------------------------
> ALTER TABLE email.mailusers
> ADD CONSTRAINT mailuser_domain_id_fkey
> FOREIGN KEY (domain_id)
> REFERENCES email.domain(id)
> ON UPDATE CASCADE
> ON DELETE RESTRICT;
> -------------------------------------
>
>
> Then I need to retrieve from psql to postfix this parameter value:
> - email adress .
> The email address is obviously something like a a concat (username,'@',domain).
You can do a simple join between the tables (the string concatenation
operator is ||):
select u.username || '@' || d.domain as email_address
from mailusers u inner join domain d on (u.domain_id = d.domain_id)
where .....
Note that "domain" is a reserved work, so you'll probably have either to
double-quote it or else rename that column to something else.
Also, you really don't need so many id-type columns... given that the
domain and username are presumably unique in their respective tables,
having additional serial and domain_id columns seems like overkill. Why
not ditch them and use the domain name and username as the primary keys?
Ray.
--
Raymond O'Donnell :: Galway :: Ireland
rod@iol.ie