最近遇到的SQL问题

select translator as '译者姓名',count(*) as '总派件次数',sum(convert(numeric(8,2),quantity)) as '总翻译字数',sum(case when DATEDIFF(mm,[date],getdate())<=6  then convert(numeric(8,2),quantity) else 0 end) as '近6个月派件字数', 
(sum(case when DATEDIFF(mm,[date],getdate())<=6  then convert(numeric(8,3),total) else 0 end)/sum(case when DATEDIFF(mm,[date],getdate())<=6  then convert(numeric(8,2),quantity) else 0 end))/0.14*100 as '近6个月平均得分'
from t_paijian where unitprice!='dd' and total!='dd'  and translation='英->中' Group by translator