Στις Wednesday 24 February 2010 15:34:48 ο/η Louis-David Mitterrand έγραψε:
> 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:
>
> drop table cruise;
> drop table cruise_type;
>
> create table cruise_type (
> id_cruise_type serial primary key,
> cruise_type_name text
> );
>
> create table cruise (
> id_cruise serial,
> id_cruise_type integer references cruise_type,
> cruise_date timestamp default now()
> );
>
> insert into cruise_type (cruise_type_name) values
> ('5 day eastern carribean cruise'),
> ('5 day western carribean cruise'),
> ('5 day eastern carribean cruise'),
> ('5 day western carribean cruise')
> ;
>
> insert into cruise (id_cruise_type) values
> (1),
> (2),
> (3),
> (4),
> (1),
> (2),
> (3),
> (4)
> ;
>
> select array_agg(ct.id_cruise_type),ct.cruise_type_name from cruise_type ct
> join cruise c on (c.id_cruise = any(array_agg)) group by cruise_type_name;
>
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
cruise_type ct, cruise c WHERE c.id_cruise_type=ct.id_cruise_type GROUP BY
ct.id_cruise_type ORDER BY ct.id_cruise_type;
id_cruise_type | List of Cruises
----------------+-----------------
1 | {1,5}
2 | {2,6}
3 | {3,7}
4 | {4,8}
(4 rows)
test=#
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 "List of
Cruises" from cruise_type ct, cruise c WHERE c.id_cruise_type=ct.id_cruise_type
GROUP BY ct.id_cruise_type,ct.cruise_type_name ORDER BY ct.id_cruise_type;
id_cruise_type | cruise_type_name | List of Cruises
----------------+--------------------------------+-----------------
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 of
the above query?
--
Achilleas Mantzios
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