优化这段代码 select o.cust_id,s.total_ordered from Orders o left join (select order_num,sum(item_price*quantity) as total_ordered from OrderItems group by order_num order by sum(item_price*quantity))s on s.order_num=o.order_num order by s.total_ordered desc;

这段代码可以进行如下优化：

1. 子查询中的 group by 和 order by 可以合并成一个语句，避免重复计算。

2. 可以在 Orders 表和 OrderItems 表上分别建立索引，以加快查询速度。

3. 可以使用 CTE（公共表表达式）来使代码更加清晰易懂。

优化后的代码如下：

WITH OrderTotals AS (
  SELECT order_num, SUM(item_price * quantity) AS total_ordered
  FROM OrderItems
  GROUP BY order_num
)
SELECT o.cust_id, s.total_ordered
FROM Orders o
LEFT JOIN OrderTotals s ON s.order_num = o.order_num
ORDER BY s.total_ordered DESC;

注意，以上优化是基于对 SQL 的一些常见优化手段，具体优化效果还需要根据具体的数据情况和数据库配置来评估。

相关问题

select Customers.cust_name,Orders.oder_num from Customers inner join Orders on Customers.cust_id == Orders.cust_id order by Customers.cust_name desc这句SQL有什么语法错误

这句 SQL 语句看起来是正确的，但是有一个小错误。在 SQL 中，"==" 不是用于比较相等的运算符，而是 " = "。因此，正确的 SQL 语句应该是：

SELECT Customers.cust_name, Orders.oder_num 
FROM Customers 
INNER JOIN Orders ON Customers.cust_id = Orders.cust_id 
ORDER BY Customers.cust_name DESC

这将按照顾客的名称（以降序排列）和订单号选择顾客和订单信息，并将它们结合在一起。

编写存储过程 SELECT a.order_id, a.done_date, a.cust_id, a.subscriber_ins_id, a.access_num, c.dev_id, c.dev_name, c.corp_org, c.company_name, c.department_code, c.department_name, c.remarks FROM JOUR1.Om_Subscriber_202301 a LEFT JOIN JOUR1.om_order_202301 b ON a.order_id = b.order_id LEFT JOIN params1.sec_developer c ON b.dev_id = c.dev_id UNION ALL SELECT a.order_id, a.done_date, a.cust_id, a.subscriber_ins_id, a.access_num, c.dev_id, c.dev_name, c.corp_org, c.company_name, c.department_code, c.department_name, c.remarks FROM JOUR1.Om_Subscriber_202302 a LEFT JOIN JOUR1.om_order_202302 b ON a.order_id = b.order_id LEFT JOIN params1.sec_developer c ON b.dev_id = c.dev_id UNION ALL SELECT a.order_id, a.done_date, a.cust_id, a.subscriber_ins_id, a.access_num, c.dev_id, c.dev_name, c.corp_org, c.company_name, c.department_code, c.department_name, c.remarks FROM JOUR1.Om_Subscriber_202303 a LEFT JOIN JOUR1.om_order_202303 b ON a.order_id = b.order_id LEFT JOIN params1.sec_developer c ON b.dev_id = c.dev_id UNION ALL SELECT a.order_id, a.done_date, a.cust_id, a.subscriber_ins_id, a.access_num, c.dev_id, c.dev_name, c.corp_org, c.company_name, c.department_code, c.department_name, c.remarks FROM JOUR1.Om_Subscriber_202304 a LEFT JOIN JOUR1.om_order_202304 b ON a.order_id = b.order_id LEFT JOIN params1.sec_developer c ON b.dev_id = c.dev_id

你可以编写一个存储过程来执行这个查询。下面是一个示例：

CREATE OR REPLACE PROCEDURE get_data AS
BEGIN
  -- 创建临时表来保存结果
  CREATE GLOBAL TEMPORARY TABLE temp_data (
    order_id          NUMBER,
    done_date         DATE,
    cust_id           NUMBER,
    subscriber_ins_id NUMBER,
    access_num        VARCHAR2(100),
    dev_id            NUMBER,
    dev_name          VARCHAR2(100),
    corp_org          VARCHAR2(100),
    company_name      VARCHAR2(100),
    department_code   VARCHAR2(100),
    department_name   VARCHAR2(100),
    remarks           VARCHAR2(100)
  ) ON COMMIT PRESERVE ROWS;

  -- 第一个查询
  INSERT INTO temp_data
  SELECT a.order_id,
         a.done_date,
         a.cust_id,
         a.subscriber_ins_id,
         a.access_num,
         c.dev_id,
         c.dev_name,
         c.corp_org,
         c.company_name,
         c.department_code,
         c.department_name,
         c.remarks
  FROM JOUR1.Om_Subscriber_202301 a
  LEFT JOIN JOUR1.om_order_202301 b
    ON a.order_id = b.order_id
  LEFT JOIN params1.sec_developer c
    ON b.dev_id = c.dev_id;

  -- 后续查询使用UNION ALL连接
  INSERT INTO temp_data
  SELECT a.order_id,
         a.done_date,
         a.cust_id,
         a.subscriber_ins_id,
         a.access_num,
         c.dev_id,
         c.dev_name,
         c.corp_org,
         c.company_name,
         c.department_code,
         c.department_name,
         c.remarks
  FROM JOUR1.Om_Subscriber_202302 a
  LEFT JOIN JOUR1.om_order_202302 b
    ON a.order_id = b.order_id
  LEFT JOIN params1.sec_developer c
    ON b.dev_id = c.dev_id;

  INSERT INTO temp_data
  SELECT a.order_id,
         a.done_date,
         a.cust_id,
         a.subscriber_ins_id,
         a.access_num,
         c.dev_id,
         c.dev_name,
         c.corp_org,
         c.company_name,
         c.department_code,
         c.department_name,
         c.remarks
  FROM JOUR1.Om_Subscriber_202303 a
  LEFT JOIN JOUR1.om_order_202303 b
    ON a.order_id = b.order_id
  LEFT JOIN params1.sec_developer c
    ON b.dev_id = c.dev_id;

  INSERT INTO temp_data
  SELECT a.order_id,
         a.done_date,
         a.cust_id,
         a.subscriber_ins_id,
         a.access_num,
         c.dev_id,
         c.dev_name,
         c.corp_org,
         c.company_name,
         c.department_code,
         c.department_name,
         c.remarks
  FROM JOUR1.Om_Subscriber_202304 a
  LEFT JOIN JOUR1.om_order_202304 b
    ON a.order_id = b.order_id
  LEFT JOIN params1.sec_developer c
    ON b.dev_id = c.dev_id;

  -- 查询结果
  SELECT * FROM temp_data;

  -- 删除临时表
  DROP TABLE temp_data;
END;
/

这个存储过程创建了一个临时表 `temp_data` 来保存查询结果，并将每个查询的结果插入到临时表中。最后，通过查询 `temp_data` 表来获取结果。

请注意，根据你的实际需求和数据库结构，你可能需要修改表和列的定义，以及查询的逻辑。确保在执行存储过程之前，已经创建了所需的表和索引。