调用好像也成功了····但是这个notice 实在不知道问题在哪儿了

修改了如下····function update($link, $data, $table, $where = null) {

foreach ( $data as $key => $val ) {
    $set .= "{$key}='{$val}',";
}
$set = trim ( $set, ',' );
$where = $where == null ? '' : ' WHERE ' . $where;
$query = "UPDATE {$table} SET {$set} {$where}";
$res = mysqli_query ( $link, $query );
if ($res) {
    return mysqli_affected_rows ( $link );
} else {
    return false;
}

}

······

这个 set我也定义了···还是会有问题= =