MySql数据库索引优化

dw_bill_detail_full_yw表已建索引字段precinctname、paidYear、paidMonth、paidDay，

EXPLAIN select precinctname,paidYear,paidMonth,paidDay,sum(chargepaid) chargepaid        from dw_bill_detail_full_yw        GROUP BY precinctname,paidYear,paidMonth,paidDay         order by precinctname,paidYear,paidMonth,paidDay;

但是提示 Using temporary; Using filesort，需要怎么优化索引？