From: Ang Chin Han <angch@bytecraft.com.my>
To: Greg Stark <gsstark@mit.edu>
Cc: Josh Berkus <josh@agliodbs.com>
Cc: Stefan Bill <sjb26@yahoo.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: LEAST and GREATEST functions?
Date: Wed, 02 Jul 2003 12:02:10 +0800
Message-ID: <3F025942.6000507@bytecraft.com.my> (raw)
In-Reply-To: <87d6gu2otf.fsf@stark.dyndns.tv>
References: <20030630201057.14507.qmail@web13905.mail.yahoo.com>
<200306302032.23113.josh@agliodbs.com>
<87d6gu2otf.fsf@stark.dyndns.tv>
Greg Stark wrote:
> MAX and MIN are single-parameter aggregate functions. LEAST and GREATEST are
> two-parameter (though in postgres they could be defined for 3 and more
> parameters) scalar functions.
If LEAST and GREATEST can accept any number of parameters, wouldn't it
make sense to code it like the way COALESCE works, rather than defining
a function for it? This way we don't need define all the various
functions with different types.
e.g.
SELECT greatest(a, b, c) FROM bar;
becomes
SELECT greatest(a, greatest(b, c)) from bar;
becomes
SELECT
CASE WHEN b < c
THEN
CASE WHEN c < a
THEN a
ELSE c
END
ELSE
CASE WHEN b < a
THEN a
ELSE b
END
END
FROM bar;
From the docs:
COALESCE and NULLIF are just shorthand for CASE expressions. They are
actually converted into CASE expressions at a very early stage of
processing, and subsequent processing thinks it is dealing with CASE.
Thus an incorrect COALESCE or NULLIF usage may draw an error message
that refers to CASE.
--
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To: pgsql-sql@postgresql.org
Cc: angch@bytecraft.com.my, gsstark@mit.edu, josh@agliodbs.com, sjb26@yahoo.com
Subject: Re: LEAST and GREATEST functions?
In-Reply-To: <3F025942.6000507@bytecraft.com.my>
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