https://stackoverflow.com/questions/2330840/mysql-invalid-use-of-group-function

出错SQL:

错误原因：

1. 不能在 WHERE 子句中使用聚合（或分组）函数

2. HAVING 只能筛选分组后的聚合结果或分组字段

# Write your MySQL query statement below
select round(sum(IF(customer_pref_delivery_date = order_date, 1, 0))/count(*), 2) as immediate_percentage
from Delivery
group by customer_id
HAVING (order_date = MIN(order_date))

修改：

SELECTROUND(SUM(IF(first_order_date = first_pref_date, 1, 0)) / COUNT(*) * 100, 2) AS immediate_percentage
FROM (SELECT customer_id,MIN(order_date) AS first_order_date,MIN(customer_pref_delivery_date) AS first_pref_dateFROM DeliveryGROUP BY customer_id
) AS first_orders;