updating table

[bberry91]

how do i update a table with only values that are entered? for example, when the admin types in the id number, and a new password, the password is updated for the user, but all other fields go to blank.

mysql_query("UPDATE members SET uname = '$uname', pword='$pword', email='$email', active='$active' WHERE ID='$ID'");

[hyperion]

mysql_query("UPDATE members SET pword='$pword' WHERE ID='$ID'"); 

mysql_query("UPDATE members SET pword='$pword', email='$email' WHERE ID='$ID'");