Re: complicated query (newbie..)

Martin Gainty wrote:
> could provide greater assistance if you could post the database schema
> you're using

Not sure what you mean by schema (I'm really new to DB world), if you
mean table descriptions from psql, here it is:

reservations=# \d hosts
Table "public.hosts"
Column | Type |
Modifiers
----------------------------+-------------------+----------------------------------------------------
id | integer | not null default
nextval('hosts_id_seq'::regclass)
ip | character varying |
hostname | character varying |
location | character varying |
architecture_id | integer |
os_kind_id | integer |
os_version_id | integer |
additional_info | character varying |
column_12 | character varying |
column_13 | character varying |
username | character varying |
password | character varying |
alias | character varying |
virtualization_id | integer |
shareable | boolean |
shareable_between_projects | boolean |
notes | character varying |
cpu | character varying |
ram | character varying |
column_24 | character varying |
batch | character varying |
asset | character varying |
owner | character varying |
ssh_key_present | character varying |
machine_type_model | character varying |
mac_address_eth_0 | character varying |
physical_box | boolean |
up_n_running | boolean |
available | boolean |
project_id | integer |
Indexes:
"hosts_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
"hosts_architecture_id_fkey" FOREIGN KEY (architecture_id)
REFERENCES architecture(id)
"hosts_os_kind_id_fkey" FOREIGN KEY (os_kind_id) REFERENCES os_kind(id)
"hosts_os_version_id_fkey" FOREIGN KEY (os_version_id) REFERENCES
os_version(id)
"hosts_project_id_fkey" FOREIGN KEY (project_id) REFERENCES project(id)
"hosts_virtualization_id_fkey" FOREIGN KEY (virtualization_id)
REFERENCES virtualization(id)

reservations=#
reservations=# \d reservation
Table "public.reservation"
Column | Type | Modifiers
--------------+-------------------+----------------------------------------------------------
id | integer | not null default
nextval('reservation_id_seq'::regclass)
start_date | date |
end_date | date |
status | character varying |
businessneed | character varying |
notetohwrep | character varying |
email_id | integer |
project_id | integer |
Indexes:
"reservation_pkey" PRIMARY KEY, btree (id)
Foreign-key constraints:
"reservation_email_id_fkey" FOREIGN KEY (email_id) REFERENCES email(id)
"reservation_project_id_fkey" FOREIGN KEY (project_id) REFERENCES
project(id)

reservations=#
reservations=# \d reservation_hosts
Table "public.reservation_hosts"
Column | Type | Modifiers
----------------+---------+-----------
reservation_id | integer |
host_id | integer |
Foreign-key constraints:
"reservation_hosts_host_id_fkey" FOREIGN KEY (host_id) REFERENCES
hosts(id)
"reservation_hosts_reservation_id_fkey" FOREIGN KEY
(reservation_id) REFERENCES reservation(id)

>
> cheers (from across the pond)
>
> Martin
> GMT+5(this week)
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>
> > Date: Thu, 9 Apr 2009 18:08:04 +0200
> > From: mrkafk(at)gmail(dot)com
> > To: sam(at)samason(dot)me(dot)uk
> > CC: pgsql-general(at)postgresql(dot)org
> > Subject: Re: [GENERAL] complicated query (newbie..)
> >
> > Sam Mason wrote:
> > > On Thu, Apr 09, 2009 at 04:47:32PM +0200, Marcin Krol wrote:
> > >> I've got 3 tables: hosts (with host.id column) and reservation (with
> > >> reservation.id column) in many-to-many relation, and
> reservation_hosts
> > >> which is an association table (with reservation_id and host_id
> columns).
> > >>
> > >> So I've got this query which selects hosts and reservations under
> > >> certain conditions:
> > >
> > > If you could describe what you want in words it would help more. I
> > > think you want something like "I was a list of all hosts and their
> first
> > > reservation that doesn't cover some specific date".
> >
> > It's somewhat complicated:
> >
> > What I'm trying to accomplish is producing list of hosts available
> > within a specified timeframe.
> >
> > What I have is a table of hosts, table of reservations (containing id,
> > start_date and end_date) and an association table reservation_hosts.
> >
> > I need a list of hosts, with accompanying reservations fulfilling
> > certain (date-related) conditions.
> >
> > But there are two twists:
> >
> > - if host has reservation(s), but those do not fulfill the date
> > conditions (the host is not available within a specified timeframe), the
> > host obviously should NOT be listed
> >
> > - if host has no reservations at all, it obviously is available, so it
> > should be listed
> >
> >
> > > If that's correct; you've got a couple of choices, either turn the
> inner
> > > join into an outer join and move it up to join onto the hosts, or get
> > > rid of it completely and use the DISTINCT ON clause.
> >
> > I'll try doing smth with it..
> >
> > Regards,
> > mk
> >
> >
> >
> >
> >
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