select dr.name, round(sum(dr.killed)/((case sum(dr.deaded) when 0 then 1 else sum(dr.deaded) end)), 2) ,round(avg(dr.assists), 2) from dota dr where dr.type=3 group by dr.name
case sum(dr.deaded) when 0 then 1 else sum(dr.deaded) end 當sum(dr.deaded)為0時取1,否則取本身
case sum(dr.deaded) when 0 then 1 else sum(dr.deaded) end 當sum(dr.deaded)為0時取1,否則取本身