//總收益
 		Order order =new Order();
        QueryWrapper<Order> queryWrapper = new QueryWrapper<Order>();
        queryWrapper.select("sum(price) as sumAll");     
        Order ord= orderService.getOne(queryWrapper);
        //注意，空指針問題
         if (ord== null){
            order.setSumAll(Double.valueOf(0)) ;
        }else{
			 order.setSumAll(ord.getSumAll());
        }

SELECT sum(price) as sumAll FROM t_order

/**
     * 總收益
     */
    @TableField(exist = false)
    private Double sumAll;

//今日總收益
   QueryWrapper<Order> queryWrapper = new QueryWrapper<Order>();
   queryWrapper.select("sum(price) as sumByToday ");
   queryWrapper.eq("TO_DAYS(create_time)","TO_DAYS(NOW())");
   Order order =new Order();
   if (orderService.getOne(queryWrapper) == null){
            order.setSumByToday(Double.valueOf(0)) ;
   }else{
            order.setSumByToday(orderService.getOne(queryWrapper).getSumByToday());
   }

  //今日總收益
        Double sumByToday =orderService.sumByToday();
        if (sumByToday == null){
            sumByToday = Double.valueOf(0);
        }
        order.setSumByToday(sumByToday);

Double sumByToday();

 @Override
    public Double sumByToday(){
        return orderMapper.sumByToday();
    }

 Double sumByToday();

 <select id="sumByToday"  resultType="java.lang.Double">
    select sum(price) as sumByToday  from t_order
     where TO_DAYS(create_time) = TO_DAYS(NOW())
    </select>

select IFNULL(sum(price),0) as sumByToday 
from t_order
where TO_DAYS(create_time) = TO_DAYS(NOW())