MySQL Order By in Right Join 子句

Question

我正在尝试像这样在 MySQL 中进行正确的连接：

SELECT customers.id,customers.firstname,customers.lastname,customers.email,orders.time,orders.notes,pendings.date_updated,pendings.issue,appointments.closed,appointments.job_description,backup_plans.expiration FROM customers
RIGHT JOIN orders
ON customers.id = orders.customer_id
ORDER BY orders.time DESC LIMIT 1
RIGHT JOIN pendings
ON customers.id = pendings.customer_id
ORDER BY pendings.date_updated DESC LIMIT 1
RIGHT JOIN appointments
ON customers.id = appointments.customer_id
ORDER BY appointments.closed DESC LIMIT 1
RIGHT JOIN backup_plans
ON customers.id = backup_plans.customer_id
ORDER BY backup_plans.expiration DESC LIMIT 1

我的意图是：选择客户的姓名和电子邮件，以及最近的订单、待处理、预约和备用计划探索。当我执行这个时，我得到一个语法错误：

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'RIGHT JOIN pendings
ON customers.id = pendings.customer_id
ORDER BY pendings.d' at line 5

我不熟悉联接，希望能提供任何帮助。

---

编辑 1：

似乎我需要按照 DanK 的建议进行子查询，如下所示：

SELECT customers.id,customers.firstname,customers.lastname,customers.email,orderstmp.time,orderstmp.notes FROM customers
RIGHT JOIN (
    SELECT orders.time,orders.notes,orders.customer_id FROM orders ORDER BY orders.time DESC LIMIT 1
) as orderstmp ON orderstmp.customer_id = customers.id

但是当我这样做时，我只得到一行结果，而我想要所有客户信息。

---

编辑 2：

根据 Tom H 的建议，我构建了这个查询：

SELECT
    customers.id,
    SQ_O.time,
    SQ_O.notes
FROM customers
LEFT JOIN (
    SELECT
        customers.id,
        orders.time,
        orders.notes
    FROM customers
    LEFT JOIN orders ON orders.customer_id = customers.id
    ORDER BY orders.time DESC LIMIT 1
) AS SQ_O ON SQ_O.id = customers.id

其中包含所有空白时间和备注字段

和

SELECT
    customers.id,
    O1.time,
    O1.notes
FROM customers
LEFT JOIN orders AS O1 ON O1.customer_id = O1.id
LEFT JOIN orders AS O2 ON O2.customer_id = customers.id AND O2.time > O1.time WHERE O2.customer_id IS NULL

达到最大执行时间。我猜这是因为与其他方言相比，我不熟悉 MySQL 中的可能性。

我也尝试过这样的相关子查询：

SELECT
    customers.firstname,
    customers.lastname,
    customers.email,
    (
        SELECT CONCAT(orders.time,': ',orders.notes)
        FROM orders
        WHERE orders.customer_id = customers.id
        ORDER BY orders.time DESC LIMIT 1
    ) as last_order
FROM customers

但“last_order”列出现空白。

---

最后，令人失望的编辑

在尝试了一些非常出色的建议后，这些建议帮助我显着地学习了 SQL，我决定编写一个 PHP 脚本来获得我想要的东西。该项目的最后期限有点过了，所以无论什么工作，工作。谢谢大家！

Answer 1

只要您可以相信没有客户拥有他们最近的两个orders 具有相同的time，这应该可以工作：

SELECT c.firstname, c.lastname, c.email, o.*
FROM customers AS c
LEFT JOIN (
   SELECT customer_id, MAX(`time`) AS maxTime
   FROM orders
   GROUP BY customer_id 
) AS lastO ON c.id = lastO.customer_id
LEFT JOIN orders AS o 
   ON lastO.customer_id = o.customer_id
   AND lastO.maxTime = o.`time`
;

只要其他表也可以依赖每个客户只有一个MAX 值，您应该能够为它们附加类似的JOINs。对于客户来说，多个相同的“最后一个”time\date_updated\closed\etc.. 的问题是它们会成倍增加结果。例如，同一客户的orders 中的相同time 对和pending 中的date_updated 对将导致4 行而不是2 行，因为orders 中该客户的每个“最后”行是与pending 中的每个“最后”行配对。

Answer 2

您可以通过子查询或额外的JOINs 来完成此操作。这是每个示例。 （注意：我使用 SQL Server，因此我习惯的某些语法可能在 MySQL 中不受支持）。我只是用 Orders 做这些示例，但希望您可以将这些想法扩展到其他表。

使用子查询：

SELECT
    C.id,
    SQ_O.time,
    SQ_O.notes
FROM
    Customers C
LEFT OUTER JOIN
(
    SELECT
        C2.Customer_ID,
        O.time,
        O.notes
    FROM
        Customers C2
    LEFT OUTER JOIN Orders O ON O.customer_id = C2.id
    ORDER BY
        O.time DESC LIMIT 1
) SQ_O ON SQ_O.customer_id = C.id

使用多个JOINs：

SELECT
    C.id,
    O1.time,
    O1.notes
FROM
    Customers C
LEFT OUTER JOIN Orders O1 ON O1.customer_id = C.id
LEFT OUTER JOIN Orders O2 ON O2.customer_id = C.id AND O2.time > O1.time
WHERE
    O2.customer_id IS NULL -- Basically we're excluding any rows where another order was found with a later time than O1

如果在 Orders.time 中完全匹配是可能的，那么您将需要额外的标准来选择一个。

Answer 3

每个查询只能有一个ORDER BY 语句。您当然可以使用子查询并将结果集引用为虚拟表，但最终在单个 SELECT 中您只能有一个 ORDER BY。

例如：

SELECT something
FROM table
ORDER BY something -- One order By

将子查询作为虚拟表：

SELECT something
FROM (SELECT anotherthing, something
      FROM table
      ORDER BY anotherthing) -- this is an order by in a separate select statement..
ORDER BY something -- still only one Order by

--------编辑--------

要获得连接语法方面的帮助，请尝试以下操作：

SELECT --fields,    
FROM customers
RIGHT JOIN orders ON customers.id = orders.customer_id
RIGHT JOIN pendings ON customers.id = pendings.customer_id
RIGHT JOIN appointments ON customers.id = appointments.customer_id
RIGHT JOIN backup_plans ON customers.id = backup_plans.customer_id
ORDER BY orders.time DESC, pendings.date_updated DESC, appointments.closed DESC, backup_plans.expiration DESC
LIMIT 1

Answer 4

试试这个：

SELECT customers.id,customers.firstname,customers.lastname,customers.email,orders.time,orders.notes,pendings.date_updated,pendings.issue,appointments.closed,appointments.job_description,backup_plans.expiration FROM customers
RIGHT JOIN orders
ON customers.id = orders.customer_id
RIGHT JOIN pendings
ON customers.id = pendings.customer_id
RIGHT JOIN appointments
ON customers.id = appointments.customer_id
RIGHT JOIN backup_plans
ON customers.id = backup_plans.customer_id
ORDER BY orders.time DESC, pendings.date_updated DESC,  appointments.closed DESC,  backup_plans.expiration DESC LIMIT 1