Select sum(x) >0 with multiple columns

[gaute]

Hi

I am writing a script to show the average value of a question in a submitted survey form.

I have 14 questions, which can have the value 1-10, if the user submitts "I don't know" it returns the value 0.

When i calculate the average it includes the value 0 but still divides with all the submitted answers (see code).

How can i make a select statement which only includes values > 0?

Current select statement:

$select = "SELECT SUM(S1), SUM(S2), SUM(S3), SUM(S4), SUM(S5), SUM(S6)
, SUM(S7), SUM(S8), SUM(S9), SUM(S10), SUM(S11)
, SUM(S12), SUM(S13), SUM(S14)
FROM Evaluering";

I want it to do something like this :

$select = "SELECT SUM(S1), SUM(S2), SUM(S3), SUM(S4), SUM(S5), SUM(S6)
, SUM(S7), SUM(S8), SUM(S9), SUM(S10), SUM(S11)
, SUM(S12), SUM(S13), SUM(S14)
WHERE S1,S2,S3,S4,S5,S6,S7,S8,S9,S10,S11,S12,S13,S14 > 0
FROM Evaluering";

Any suggestions?