Comparing data between years

Hello, 
 
I've got a SQL table storing some fluid quantities aggregated by year, origin and type : 
<pre class='_prettyXprint _lang-auto _linenums:0'>year | type | origin | quantity</pre>
 
What I'd like to have is a report showing for each origin, and each fluid type not only the quantity, but also its evolution compared to the previous year quantity : 
 
<pre class='_prettyXprint _lang-auto _linenums:0'>
Report for year 2008

Origin : raw fluid
Type: CFC R-11 | 25 (+25%)
Type: CFC R-10 | 11 (+10%)
</pre>
Grouping the data is ok for me but I cannot figure a way to get the percentage showing the evolution. Is there some mechanism in BIRT htat could help me ? 
 
Thanks

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Comments

mwilliams

Hi rhumaric,

If I understand your problem correctly, you should just be able to store the previous year's value in a variable and use that value in the next year's table to do your calculation.