Update mysql without replacing empty fields - php

Question

I'm trying to do an update without replace the empty fields, for examplo, if i have field number 1 and it is empty nothing happens in database but if field number 2 has some content i want it to be updated. the thing happens is when i do it the empty field goes to the database and REPLACE the content of the field for an empty value.
I need an example of how can i do it.
PD: I am using PHP OOP.
This is my query:
$conio = "UPDATE affiliates SET nickname = '$nickname', fullname = '$fullname' , email = '$email', skype = '$skype', country = '$country', address = '$address', city = '$city', zip = '$zip', bankname = '$bankname', bankaccount = '$bankaccount', beneficiary = '$beneficiary', username = '$username', password = '$password', whene = '$whene' WHERE id = '$users'";
mysqli_query($this->link, $conio) or die (mysqli_error($this->link));

Answer 1

Example: If you want to update the input where the value is not null.
<?php
...
$sql = "UPDATE affiliates SET ";
$sql_where = "WHERE id = '$users'";
$sql_set = "";
$firstName = $_POST['firstName'];
if(!empty($firstName))
$sql_set .= "firstName = '$firstName',";
$lastName = $_POST['lastName'];
if(!empty($lastName))
$sql_set .= "lastName = '$lastName',";
and the same thing for all the other inputs ...
...
mysql_query($sql.$sql_set.$sql_where);
Of course there are better ways of writing this code (ex: using for loop on elements of $_POST), but that's the concept, ...