Re: transposing data for a view - Mailing list pgsql-sql

I think this might do the trick...

CREATE FUNCTION hori_view() RETURNS BOOLEAN AS 'DECLARE view_select TEXT; view_from TEXT; view_where TEXT; column_name
TEXT;last_column_name TEXT; g_row generalized_table%ROWTYPE;BEGIN SELECT region INTO column_name    FROM
generalized_tableORDER BY region LIMIT 1; view_select := ''SELECT '' || column_name ||     ''.scanid, '' || column_name
||''.volume AS "'' ||     column_name || ''_volume"''; view_from := '' FROM generalized_table '' || column_name;
view_where:= '' WHERE '' ||column_name ||     ''.region = '''''' || column_name || ''''''''; last_column_name :=
column_name;FOR g_row IN SELECT DISTINCT ON (region) *    FROM generalized_table ORDER BY region OFFSET 1 LOOP
view_select:= view_select || '', '' || g_row.region ||    ''.volume AS "'' || g_row.region || ''_volume"'';
view_from:= view_from || '' JOIN generalized_table '' ||        g_row.region || '' ON ('' || last_column_name ||
''.scanid= '' || g_row.region || ''.scanid)'';    view_where := view_where || '' AND '' || g_row.region ||
''.region= '''''' ||  g_row.region || '''''''';    last_column_name := g_row.region; END LOOP;EXECUTE ''CREATE VIEW
generalized_viewAS '' || view_select ||        view_from || view_where;RETURN TRUE;      END;
 
' LANGUAGE 'plpgsql';

SELECT hori_view();

SELECT * FROM generalized_view;

Ok, it may not be pretty but it works,

Regards,

Aasmund.

On Wed, 31 Oct 2001 12:42:10 -0800, "Josh Berkus" <josh@agliodbs.com> wrote:
> Jeremy,
> 
> First, to do a pivot table, you have to be using Postgres 7.1.x.  7.0.x
> will not do it.  So upgrade now.
> 
> 
> There are two approaches, the simple approach and the complex.  The
> simple approach requires you to know in advance of building the view all
> of the possible values for your category column.  The complex approach,
> which is dynamic, requires a rather sophisticated function (which I will
> write eventually, really!) so we won't go into it here.
> 
> The simple approach is to create each column as a sub-select in the FROM
> clause of your statement.  So, per the example above:
> 
> SELECT scanid, A_volume, B_volume, C_volume
> FROM (SELECT scanid FROM volumes GROUP BY scanid) scan
> LEFT OUTER JOIN
> (SELECT scanid, volume as A_volume FROM volumes WHERE region = 'A') av
> ON scan.scanid = av.scanid LEFT OUTER JOIN
> (SELECT scanid, volume as B_volume FROM volumes WHERE region = 'B') bv
> ON scan.scanid = bv.scanid LEFT OUTER JOIN
> (SELECT scanid, volume as C_volume FROM volumes WHERE region = 'C') cv
> ON scan.scanid = cv.scanid
> ORDER BY scanid;
> 
> This approach can be adapted to include aggregates and the like.
> 
> -Josh Berkus
> 
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Aasmund Midttun Godal

aasmund@godal.com - http://www.godal.com/
+47 40 45 20 46