posting NULL from a form

[Anon]

I have a slight problem. On a form I have created, there are text fields where the user has to either enter a number or leave it blank. These values are posted to a db and are used for calculating an average. The problem is that if the user leaves a field blank, the value of that field comes into the database as a zero. Since these numbers are used to calculate averages, the zeros throw everything off. Is there a way to make these form values post as NULLs instead of zeros? Thanks in advance.

[bastien]

Why not just change the SQL to only avg the numbers that are not 0?

But the answer is to
a) allow the DB field to be null, with no default
b) put some if...then statements to have a look at the value from the text box and if it is not null then insert the value...

$sql= "insert into table values("
if (isset($field)) {
$sql=$sql." $field,"
}
$sql=$sql." $anotherfield, $3rdField")

hth

bastien