where in 专题

查找一个字段，通常是通过主键回表带回，需避免没有带回的写法。

力扣1174：

# 1.首次订单
with tmp as 
(select *
from Delivery
where (customer_id,order_date) in
    (select customer_id,min(order_date)
    from Delivery
    group by customer_id))

# 1.1即时订单
,tmp1 as 
(select count(*) as count_immediate
from tmp
where order_date = customer_pref_delivery_date)

# 1.2总订单
,tmp2 as
(select count(*) as count_total
from tmp)

# 2.查询结果
select distinct round(count_immediate/count_total*100,2) 
    as immediate_percentage 
from tmp,tmp1,tmp2

-END