compare sales with previous year sales

Hello all,

I am old on this forum but my experience is still very less and every year I renew thinking that I will devote time to learn it but every year i cannot find enough time. By saying that I need assistance here.

I am trying to compare my sales data from DailyReport table with previous year same date. I created a custom button but dont know how should i construct the sql statement. also after doing that this report has to be emailed with cc option, all in HTML format.

pls help.