select t1.sales_reg,t1.pack_cod,(100-(((t1.total)-(t2.total))*100)/t1.total) as ret_per 
  from (
    select sales_reg,pack_cod,sum(pre_ret+post_ret)as total
      from projection
      where no_of_mon =1
      group by sales_reg,pack_cod
      having sum(pre_ret+post_ret)>100
  ) as t1,(
    select sales_reg,pack_cod,sum(pre_ret+post_ret) as total
      from projection
      where no_of_mon =2
      group by sales_reg,pack_cod
      having sum(pre_ret+post_ret)>100
  ) as t2
  where t1.sales_reg=t2.sales_reg and t1.pack_cod=t2.pack_cod and t1.total>=t2.total
  order by 3 desc
  limit 5;