PHP计算while循环中两个值之间的差异

Question

I'm outputting an XML document with PHP from mysql results, in one column I have a bunch of values, but these are accumulative values, i.e.: 1,3,6,8,12,45,etc...but how can I only echo out the difference between values rather than the values themselves in this:

while($row = mysql_fetch_array($result)){
    $strXML .= "<set name='".date("G:i:s", strtotime($row["tstamp"]))
            .  "' value='".$row['steam']."' color='AFD8F8' />";
}

The column in question is "steam", how could I go about doing this?

Answer 1

Do you want to do this?

$previous = 0;
while($row = mysql_fetch_array($result)){
    $difference = $row['steam'] - $previous;
    $strXML .= "<set name='".date("G:i:s", strtotime($row["tstamp"]))
            .  "' value='".$difference."' color='AFD8F8' />";
    $previous = $row['steam'];
}

assuming $row['steam'] is a single number, not a comma separated list.