How to obtain % from db records

Hi phpers!

I extract some values from a db as these:

2014 46
2013 57
2011 29
2010 89

Now, my goal is to calculate the percentage change in a year than the previous year in order to obtain this:

2014 46 -19%
2013 57 +96%
2011 29 -67%
2010 89

My code is actually;

$myquery = mysql_query("SELECT Year, Sales FROM Mytable");

while ($row = mysql_fetch_array($myquery)) {
	echo $row['Year'] . ' ' . $row['Sales'];
}

Can you help me please? thanks

First, simplify. Imagine that you have this array:

$values = [46, 57, 29, 89];

For each of the elements other than the last one, you want to compute: ($current - $next) / $current.

How would you go about doing this?

Before you try that calculation with the array as laserlight suggested, you'll need to make sure that the values are sorted by year:

SELECT Year, Sales FROM Mytable ORDER BY Year