如何使用单个查询更新多个字段？

Question

我正在与一家公司注册会员的MLM公司合作，如果发现任何数据错误，它必须再次更新会员的数据。

我有正确的代码，当所有字段都必须更新时效果很好但问题是它不适用于单个输入框。请给我解决这个问题。

<?php
if(isset($_POST['update'])) {
    $dbhost = 'localhost';
    $dbuser = 'vvvv';
    $dbpass = 'xxxx';
    $conn = mysql_connect($dbhost, $dbuser, $dbpass);
    if(! $conn ) {
        die('Could not connect: ' . mysql_error());
    }
    $usrid = $_POST['uid'];
    $pwrd = $_POST['pwd'];
    $nm = $_POST['noe'];
    $fnm = $_POST['fn'];
    $addrs = $_POST['adrs'];
    $cntn = $_POST['cnt_no'];
    $cty = $_POST['ct'];
    $sql = "UPDATE office_user ".
        "SET
            password = '$pwrd',
            name='$nm',
            father_name='$fnm',
            address='$addrs',
            contact_no='$cntn',
            city='$cty' ".
        "WHERE user_id = '$usrid'" ;

    mysql_select_db('my_db');
    $retval = mysql_query( $sql, $conn );
    if(! $retval ) {
        die('Could not update data: ' . mysql_error());
    }
    echo "Updated data successfully\n";
    mysql_close($conn);
}
?>