如何解决 MySQL 中的'视图的 SELECT 在 FROM 子句中包含子查询”错误？

Error: View's SELECT Contains a Subquery in the FROM Clause

问题描述：

您正在尝试创建一个视图，但遇到错误“视图的 SELECT 语句包含 FROM 子句中的子查询”。您提供的查询如下：

create view view_credit_status as 
(select credit_orders.client_id, 
        sum(credit_orders.number_of_credits) as purchased, 
        ifnull(t1.credits_used,0) as used 
 from credit_orders
 left outer join (select * from (select credit_usage.client_id, 
                                        sum(credits_used) as credits_used 
                                 from credit_usage 
                                 group by credit_usage.client_id) as t0
                  ) as t1 on t1.client_id = credit_orders.client_id
 where credit_orders.payment_status='Paid'
 group by credit_orders.client_id)

原因：

根据 MySQL 文档，SELECT 语句不能在 FROM 子句中包含子查询。

解决方案：

您的解决方法是为每个子查询创建视图。然后，您可以从视图 view_credit_status 中访问这些视图。

# 创建包含子查询的视图：
create view sum_credit_usage as
select client_id, sum(credits_used) as credits_used
from credit_usage 
group by client_id;

# 创建您的最终视图：
create view view_credit_status as 
(select credit_orders.client_id, 
        sum(credit_orders.number_of_credits) as purchased, 
        ifnull(sum_credit_usage.credits_used, 0) as used 
 from credit_orders
 left outer join sum_credit_usage on t1.client_id = credit_orders.client_id
 where credit_orders.payment_status='Paid'
 group by credit_orders.client_id);

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