From: Achilleas Mantzios <achill@matrix.gatewaynet.com>
Organization: Dynacom Tankers Mgmt
To: pgsql-sql@postgresql.org
Subject: Re: join with an array
Date: Wed, 24 Feb 2010 16:39:00 +0200
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=CE=A3=CF=84=CE=B9=CF=82 Wednesday 24 February 2010 15:34:48 =CE=BF/=CE=B7 =
Louis-David Mitterrand =CE=AD=CE=B3=CF=81=CE=B1=CF=88=CE=B5:

> Here is a test case I built. I want to list all cruises by cruise_type
> but after merging cruise_type that have the same cruise_type_name:
>=20
> drop table cruise;
> drop table cruise_type;
>=20
> create table cruise_type (
>     id_cruise_type serial primary key,
>     cruise_type_name text
> );
>=20
> create table cruise (
>     id_cruise serial,
>     id_cruise_type integer references cruise_type,
>     cruise_date timestamp default now()
> );
>=20
> insert into cruise_type (cruise_type_name) values=20
> ('5 day eastern carribean cruise'),
> ('5 day western carribean cruise'),
> ('5 day eastern carribean cruise'),
> ('5 day western carribean cruise')
> ;
>=20
> insert into cruise (id_cruise_type) values=20
> (1),
> (2),
> (3),
> (4),
> (1),
> (2),
> (3),
> (4)
> ;
>=20
> select array_agg(ct.id_cruise_type),ct.cruise_type_name from cruise_type =
ct join cruise c on (c.id_cruise =3D any(array_agg)) group by cruise_type_n=
ame;
>=20

You dont specify (in english) what you exactly want to achive, but here is =
my shot:
1st, get the cruises by cruise type:
select ct.id_cruise_type,array_agg(c.id_cruise) as "List of Cruises" from c=
ruise_type ct, cruise c WHERE c.id_cruise_type=3Dct.id_cruise_type GROUP BY=
 ct.id_cruise_type ORDER BY ct.id_cruise_type;
 id_cruise_type | List of Cruises
=2D---------------+-----------------
              1 | {1,5}
              2 | {2,6}
              3 | {3,7}
              4 | {4,8}
(4 rows)

test=3D#  =20
Then you may pretify this to include the name of each cruise type as well:

select ct.id_cruise_type,ct.cruise_type_name,array_agg(c.id_cruise) as "Lis=
t of Cruises" from cruise_type ct, cruise c WHERE c.id_cruise_type=3Dct.id_=
cruise_type GROUP BY ct.id_cruise_type,ct.cruise_type_name ORDER BY ct.id_c=
ruise_type;
 id_cruise_type |        cruise_type_name        | List of Cruises
=2D---------------+--------------------------------+-----------------
              1 | 5 day eastern carribean cruise | {1,5}
              2 | 5 day western carribean cruise | {2,6}
              3 | 5 day eastern carribean cruise | {3,7}
              4 | 5 day western carribean cruise | {4,8}
(4 rows)

EXERCISE:
Why cant we exclude ct.id_cruise_type from the select clause and group by o=
f the above query?

=2D-=20
Achilleas Mantzios