Not updating certain fields in same row

Hi everyone,

I am attempting to update a record for a login system while leaving  
certain fields untouched if they arn't changed, and am running into  
issues.

Basically what I want to do, is say I have these fields:

Field1
Field2
Field3
Field4

I update Field1 and Field3 but not Field2 and Field4. What I want to  
do is change the values in Field1 and Field3 without touching the  
values in Field2 and Field4.

I have tried this code:
		$tab = "\t";
	if (!isset($_POST['txtLoginName']) || empty($_POST['txtLoginName'])) {
		
			$loginName = mysqli_real_escape_string($chpwpostlink,  
$_POST['txtLoginName']);
		}
		else
		{
			$loginName = $tab;
		}

which works the fields that I've changed, but if I don't submit a  
value in the form it sets the field to be blank in MySQL. Which is  
what I am trying to avoid. Any ideas?

--

Jason Pruim
Raoset Inc.
Technology Manager
MQC Specialist
3251 132nd ave
Holland, MI, 49424-9337
www.raoset.com
[email protected]