Message-ID: <003a01c6215d$6a9320a0$0600000a@matt.mutua>
Reply-To: <ipv@tinet.org>
From: <ipv@tinet.org>
To: <pgsql-sql@postgresql.org>
References: <dr6jv0$emi$2@news.hub.org>
Subject: Re: sorting by day of the week
Date: Wed, 25 Jan 2006 04:14:12 +0100
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Hi,

Try to use a calculated index:

(tested similar solution, but not this code)


CREATE OR REPLACE FUNCTION TestOrder (nameTable.weekDay%TYPE) RETURNS INT AS 
'

DECLARE

numWeekDay INT;

BEGIN

if ($1 = ''Wed'') then numWeekDay := 1;

if ($1 = ''Tue'') then numWeekDay := 2;

.....

RETURN (numWeekDay);

END;

' LANGUAGE 'plpgsql' STRICT IMMUTABLE;


CREATE INDEX idx_TestOrder

ON nameTable USING btree (TestOrder(nameTable.weekDay));


SELECT * FROM trajecte ORDER BY TestOrder(nameTable.weekDay);


Regards


----- Original Message ----- 
From: "Joseph Shraibman" <jks@selectacast.net>
To: <pgsql-sql@postgresql.org>
Sent: Wednesday, January 25, 2006 2:23 AM
Subject: [SQL] sorting by day of the week


> p8:owl=>SELECT to_char( logtime, 'Dy'),count(*) FROM logtab WHERE 
> date_trunc('day', logtime) > current_date + '7 day ago'::interval group by 
> to_char( logtime, 'Dy') ORDER BY to_char( logtime, 'Dy') DESC;
>  to_char | count
> ---------+-------
>  Wed     |  1447
>  Tue     |   618
>  Thu     |  1161
>  Sun     |   230
>  Sat     |   362
>  Mon     |   760
>  Fri     |  1281
> (7 rows)
>
> The problem is that I want those results sorted in day of week order, not 
> text order of the day name, so I tried this:
>
> p8:owl=>SELECT to_char( logtime, 'Dy'),count(*) FROM sclog WHERE 
> date_trunc('day', logtime) > current_date + '7 day ago'::interval group by 
> to_char( logtime, 'Dy') ORDER BY to_char( logtime, 'D') DESC;
> ERROR:  column "sclog.logtime" must appear in the GROUP BY clause or be 
> used in an aggregate function
>
> Now obviously I don't want to group by logtime (a timestamp) so how do I 
> work around this?  What I really need is a function that converts from the 
> char representation to a day of week number or vice versa.  I also have 
> the same problem with month names.
>
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