Null X Zero问题

Ok, this is driving me crazy!! Got a MySQL table with an integer field default set to null. Need to update it through a form submission. If form field is blank, set database field to NULL, ELSE set database field to form submission value.

So, in PHP I have: (staging code, still needs to be sanitized)

if($_POST['vendor-product'] != ''){
    $ms2VendorID = $_POST['vendor-product'];
}else{
    $ms2VendorID = '';
}

The problem is that instead of NULL it enters a zero. I've tried several different ways and nothing seems to be working.

Thanks for any help.

Why don't you assign NULL (as a string) to your variable in the else statement?

if($_POST['vendor-product'] != ''){
    $ms2VendorID = $_POST['vendor-product'];
}else{
    $ms2VendorID = "NULL";
}

Also, make sure that the field has not the NOT NULL constraint enabled.