MyBatis查询返回map类型

//DAO层返回的结果为list
public List
 
  > queryItemSaleCountBatch() {   
    return selectList("selectByField");
}

//mybatis片段

   select t.item_id as itemId, sum(t.`quantity`) as saleNum from order t where t.order_status = 1 group by t.item_id