题解 | 统计各等级会员用户下订单总额

方法一：case when

select u.vip,sum(case when o.order_price is null then 0 else o.order_price end) as order_total
from uservip_tb u left join order_tb o on u.user_id = o.user_id
group by u.vip
order by order_total desc

方法二：if

select u.vip,sum(if(o.order_price,o.order_price,0)) as order_total
from uservip_tb u left join order_tb o on u.user_id = o.user_id
group by u.vip
order by order_total desc

方法三：coalesce

select u.vip,sum(coalesce(o.order_price,0)) as order_total
from uservip_tb u left join order_tb o on u.user_id = o.user_id
group by u.vip
order by order_total desc

方法四：ifnull

select u.vip,sum(ifnull(o.order_price,0)) as order_total
from uservip_tb u left join order_tb o on u.user_id = o.user_id
group by u.vip
order by order_total desc