To: vince@weaktight.com
cc: pgsql-sql@postgresql.org
Subject: Re: query; check for zero and floats 
In-reply-to: <20060401010317.tbza82opw0c0ccg0@webmail.weaktight.com> 
References: <20060401010317.tbza82opw0c0ccg0@webmail.weaktight.com>
Comments: In-reply-to vince@weaktight.com
	message dated "Sat, 01 Apr 2006 01:03:17 -0500"
Date: Sat, 01 Apr 2006 01:32:39 -0500
Message-ID: <8347.1143873159@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

vince@weaktight.com writes:
> I'm trying to do a simple query and I'm not sure how to get it to work:
> SELECT SUM(x0 + y0 + z0) / SUM(x2 + y2) AS A1, SUM(x1 + y1 + z1) / SUM(x3 + y3)
> AS A2
> FROM test

> 1. All variables are integers.  When it does the division, it returns an
> integer, but I want a float.  (I've tried numerous things to no avail)

Cast one or both division inputs to float.

> 2. If SUM(x2 + y2) == 0; there is a divide by zero error.  How do I check and
> pass on zeroes?

Add a HAVING condition (not WHERE, because you need to filter on the
post-aggregation status).

I think you want

SELECT SUM(x0 + y0 + z0)::float / SUM(x2 + y2) AS A1,
       SUM(x1 + y1 + z1)::float / SUM(x3 + y3) AS A2
FROM test
HAVING SUM(x2 + y2) <> 0

(maybe also having SUM(x3 + y3) <> 0)

			regards, tom lane