Trying to make a new table by pulling data from two tables and keep getting 'Error: Every derived table must have its own alias' on this query

Question

我有一个 'Orders' table 和一个 'Records' table。

订单 table 有以下列：

order_id       order_date        seller        order_price

记录 table 有以下列：

order_id        record_created_at         record_log

我正在尝试提取和编译以下数据列表，但我不断收到错误消息：

order_week
seller
total_num_orders
under100_count --this is the number of orders that were < 0
over100_count --this is the number of order that >= 0
approved --this is the number of orders that were approved by the payment platform

这是我的查询：

SELECT order_week, seller, total_num_orders, under100_count, over100_count, approved
FROM (

    SELECT 
        EXTRACT(WEEK FROM order_created_at) AS order_week,
        merchant_name AS seller, 
        COUNT(merchant_name) AS total_num_orders,
        SUM(DISTINCT total_order_price < 100) AS under100_count,
        SUM(DISTINCT total_order_price >= 100) AS over100_count
    FROM orders o
    GROUP BY order_week, seller)

INNER JOIN (

    SELECT
        COUNT(DISTINCT o.order_id) AS approved
    FROM records r
    WHERE record_log = 'order approved'
    GROUP BY order_id)

ON l.order_id = o.order_id;

我做错了什么？

Answer 1

join 中的子查询需要一个别名。它还需要 return order_id 列，以便可以加入。

inner join ( select order_id, ... from records ... group by order_id) r  --> here
on l.order_id = o.order_id

我实际上会将您的查询写成：

select 
    extract(week from o.order_created_at) as order_week,
    o.merchant_name as seller, 
    count(*) as total_num_orders,
    sum(o.total_order_price < 100) as under100_count,
    sum(o.total_order_price >= 100) as over100_count,
    sum(r.approved) approved
from orders o
inner join (
    select order_id, count(*) approved
    from records r
    where record_log = 'order approved'
    group by order_id
) r on r.order_id = o.order_id;
group by order_week, seller, approved

理由：

您不需要，也不需要，distinct 在这里的聚合函数中；它效率低下，甚至可能产生错误的结果
count(*) 效率更高 count(<expression>) - 所以，使用它，除非你知道为什么要这样做
我去掉了一层不必要的嵌套

如果有没有记录的订单，您可能需要 left join。

Trying to make a new table by pulling data from two tables and keep getting 'Error: Every derived table must have its own alias' on this query

Trying to make a new table by pulling data from two tables and keep getting 'Error: Every derived table must have its own alias' on this query

mysql

sql

join

count

subquery