Thread: Need a SQL to create sets of hobbies

Hi!

CREATE TABLE x1 (name TEXT, hobby TEXT, PRIMARY KEY(name,hobby));

INSERT INTO x1 VALUES('John','music');
INSERT INTO x1 VALUES('John','arts');
INSERT INTO x1 VALUES('Bob','arts');
INSERT INTO x1 VALUES('Bob','music');
INSERT INTO x1 VALUES('Rocky','copmputer');
INSERT INTO x1 VALUES('Steve','arts');
INSERT INTO x1 VALUES('Steve','football');
INSERT INTO x1 VALUES('Tom','computer');
INSERT INTO x1 VALUES('Tom','music');

select * from x1;
name  |  hobby   
-------+----------John  | musicJohn  | artsBob   | artsBob   | musicRocky | computerSteve | artsSteve | footballTom   |
computerTom  | music
 
(9 rows)

John and Bob have the same hobbies - music and arts. So music and arts
are treated as one set of hobbies.

Rocky has an unique set of interest - computer.

Steve also likes arts just as John and Bob do, but he also has an
exclusive interest - football. Thus, his set of hobbies is unique -
arts, football.

One of Tom's hobbies, music, overlaps those of John, Bob, and Rocky; but
computer does not. Hence his hobbies, computer and music, forms a new
set of hobbies.

Now we have 4 sets of hobbies:

set 1: music, arts
set 2: computer
set 3: arts, football
set 4: computer, music

I am looking for an SQL that creates sets of hobbies in table x2 by
selecting from table x1:

CREATE TABLE x2 (sid INTEGER, hobby TEXT, PRIMARY KEY(sid,hobby));

and makes x2 contain rows:
sid   |  hobby   
-------+----------
1      | music
1      | arts
2      | computer
3      | arts
3      | football
4      | computer
4      | music

where gid starts from 1.

Thank you in advance!
CN

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In article <1158729519.6421.271361727@webmail.messagingengine.com>,
"CN" <cnliou9@fastmail.fm> writes:

> select * from x1;

>  name  |  hobby   
> -------+----------
>  John  | music
>  John  | arts
>  Bob   | arts
>  Bob   | music
>  Rocky | computer
>  Steve | arts
>  Steve | football
>  Tom   | computer
>  Tom   | music
> (9 rows)

> Now we have 4 sets of hobbies:

> set 1: music, arts
> set 2: computer
> set 3: arts, football
> set 4: computer, music

> I am looking for an SQL that creates sets of hobbies in table x2 by
> selecting from table x1:

> CREATE TABLE x2 (sid INTEGER, hobby TEXT, PRIMARY KEY(sid,hobby));

> and makes x2 contain rows:

>  sid   |  hobby   
> -------+----------
> 1      | music
> 1      | arts
> 2      | computer
> 3      | arts
> 3      | football
> 4      | computer
> 4      | music

> where gid starts from 1.

You could use something like that:
 CREATE TEMP TABLE tmp (   id SERIAL NOT NULL,   name TEXT NOT NULL,   PRIMARY KEY (id) );
 INSERT INTO tmp (name) SELECT DISTINCT ON (ARRAY (          SELECT y1.hobby          FROM x1 y1          WHERE y1.name
=y2.name          ORDER BY y1.name, y1.hobby        ))        y2.name FROM x1 y2;
 
 INSERT INTO x2 (sid, hobby) SELECT tmp.id, x1.hobby FROM tmp JOIN x1 ON x1.name = tmp.name;

On 9/20/06, CN <cnliou9@fastmail.fm> wrote:)

person_hobby (
   person_id,
   hobby_id
)

Then you can get the list of hobbies for each person like this:

    SELECT
        person.person_id,
        array(
            SELECT hobby_name
            FROM person_hobby
            INNER JOIN hobby ON (hobby.hobby_id = person_hobby.hobby_id)
            WHERE person_hobby.person_id = person.person_id
            ORDER BY hobby_name
        ) AS hobby_list
    FROM person

Then do this to flatten it back out:

SELECT
    -- Gives you a unique id though using a SERIAL on a table would be better
    min(mysub.person_id), 
    hobby.hobby_name
FROM (
    SELECT
        person.person_id,
        array(
            SELECT hobby_name
            FROM person_hobby
            INNER JOIN hobby ON (hobby.hobby_id = person_hobby.hobby_id)
            WHERE person_hobby.person_id = person.person_id
            ORDER BY hobby_name
        ) AS hobby_list
    FROM person
) mysub
INNER JOIN person_hobby ON (person_hobby.person_id = mysub.person_id)
INNER JOIN hobby ON (hobby.hobby_id = person_hobby.hobby_id)
GROUP BY
    mysub.hobby_list,
    hobby.hobby_name

I did not try it so it may require a little tweaking to work.  Also, I don't know what the performance would be like.

==================================================================
   Aaron Bono
   Aranya Software Technologies, Inc.
   http://www.aranya.com
   http://codeelixir.com
==================================================================