query; check for zero and floats - Mailing list pgsql-sql

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

Problems:

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)

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

Thanks,
Vince.