RE: [GENERAL][SQL] 'denormalising' with a select

Here is a version using aggregation:

create function get_codes_agf(text, text) returns text as '
begin
if (length($1) > 0) then
return $1 || '', '' || $2
else
return $2;
end if;
end' language 'plpsql';

CREATE AGGREGATE get_codes_ag (
sfunc1 = get_codes_agf,
basetype = text,
stype1 = text,
initcond1 = ''
);

select brecard_id, get_codes_ag(code) from table_name group by brecard_id;

> > -----Original Message-----
> > From: Stuart Rison [SMTP:stuart(at)ludwig(dot)ucl(dot)ac(dot)uk]
> > Sent: Tuesday, June 01, 1999 6:54 AM
> > To: pgsql-general(at)postgreSQL(dot)org
> > Subject: [GENERAL][SQL] 'denormalising' with a select
> >
> > Hi there,
> >
> > This was posted to SQL where it 'truly' belongs but I got no answwer and
> > since it has a bit of database design in it (and a lot more people seem
> to
> > read [GENERAL]) I thought I'd try it here.
> >
> > Consider a table like this:
> >
> > brecard_id |code
> > ----------------+----
> > IEGA18051999006 |COME
> > IPHA04031999004 |CRIB
> > IPHA04031999005 |COME
> > IPHA04031999005 |CRIB
> > IPHA26021999006 |SOLI
> > IPHA26021999010 |COME
> > IPHA26021999010 |SOLI
> > ISTL04031999001 |CRIB
> > IUCH03031999003 |COME
> > IUCH03031999003 |CRIB
> > IUCH03031999003 |MICR
> > IUCH03031999003 |SOLI
> >
> > each combination of id and code is unique (they form a composite primary
> > key)
> > but any brecard_id could have 1 or more codes associated with it
> > (theoretically with no upper boundary but let us say a maximum of 5
> > codes).
> >
> > Is there a SELECT which will turn each of the codes for one brecard_id
> > into
> > a column... ie.
> >
> > brecard_id |code1|code2|code3|code4|code5
> > ----------------+-----+-----+-----+-----+-----
> > IEGA18051999006 |COME | | | |
> > IPHA04031999004 |CRIB | | | |
> > IPHA04031999005 |COME |CRIB | | |
> > IPHA26021999006 |SOLI | | | |
> > IPHA26021999010 |COME |SOLI | | |
> > ISTL04031999001 |CRIB | | | |
> > IUCH03031999003 |COME |CRIB |MICR | |
> > IUCH03031999003 |SOLI | | | |
> >
> > and here a a few more brainteasers for you gurus out there...
> >
> > 1) I'm actually not fussed about the order the codes appear in the
> > columns,
> > but let's say the order mattered, would this affect the SELECT(s)?
> > 2) Would it make the query easier if I knew the maximum number of codes
> > one
> > brecard_id could have?
> > 3) (this one for true Wizards -and Sorceresses, Herouth ;)- only) Could
> > you
> > write a 'generalised' query which could cope with tables having variable
> > 'maximum' numbers of codes associated with each brecard_id?
> >
> > For the life of me I don't know how you'd do it in SQL, I have PL/pgSQL
> > and
> > have started playing around with that but I'd hate to re-invent the
> wheel!
> >
> > regards,
> >
> > Stuart.
> >
> > +-------------------------+--------------------------------------+
> > | Stuart Rison | Ludwig Institute for Cancer Research |
> > +-------------------------+ 91 Riding House Street |
> > | Tel. (0171) 878 4041 | London, W1P 8BT, UNITED KINGDOM. |
> > | Fax. (0171) 878 4040 | stuart(at)ludwig(dot)ucl(dot)ac(dot)uk |
> > +-------------------------+--------------------------------------+