Re: Need a SQL to create sets of hobbies

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;