sql - 按查询挑战分组

Question

我有这些表:

customer
--------
customer_id int
name        varchar(255)

order
-----
order_id    int
customer_id int
discount    boolean

我可以通过如下查询获取每个客户的订单数量:

select c.id, count(o.order_id)
from customer c 
left join order as o using c.customer_id = o.customer_id
group by 1

或者，我可以通过以下方式获取每个客户的打折订单数量:

select c.id, count(o.order_id)
from customer c 
left join order as o using c.customer_id = o.customer_id and o.discount = true
group by 1

但我想不出一种在单个查询中同时获得两者的方法。我尝试了以下方法:

select c.id, count(o.order_id), count(o2.order_id)
from customer c 
left join order as o using c.customer_id = o.customer_id
left join order as o2 using c.customer_id = o2.customer_id and o2.discount = true
group by 1

但是没有用。是否可以在单个 (MySql) 查询中计算两者？

干杯， 唐

Answer 1

怎么样

select c.id, count(o.order_id),sum(if(o.discount,1,0))
from customer c 
left join order as o using c.customer_id = o.customer_id
group by c.id