[英]MySQL Join Without Duplicates
I have a customers table, and an orders table. 我有一个客户表和一个订单表。 Each customer can have many orders. 每个客户可以有很多订单。
I want to select every customer, along with their earliest order number from the orders table (it is important that I select the earliest order number, not just any order). 我想从订单表中选择每个客户及其最早的订单号(重要的是选择最早的订单号,而不仅仅是任何订单)。 I want to list customers whether they have an order or not, and I don't want to include customers twice if they have more than one order. 我想列出客户是否有订单,如果客户有多个订单,我不想两次包含客户。
I'm using this: 我正在使用这个:
SELECT *
FROM customers
LEFT JOIN orders
ON customers.id = orders.customer_id
GROUP BY customers.id
This gives me almost what I want, except it will pick whatever order ID it likes from the table. 这几乎给了我想要的东西,除了它会从表中选择喜欢的任何订单ID。 I need to be able to sort, and pick the smallest order ID. 我需要能够排序,并选择最小的订单ID。
Any ideas please? 有什么想法吗?
Im pretty sure its something that's staring me in the face... 我很确定这是让我盯着我的脸...
EDIT: Tables' Structures as requested 编辑:表的结构按要求
Customers: 顾客:
| ID | Name | Address | Etc | ---------------------------------------- | 1 | Joe | 123 Fake Street | | | 2 | Mike | 1600 Fake Road | | | 3 | Bill | Red Square, Moscow | | ----------------------------------------
Orders: 命令:
| ID | Customer_ID | Date | --------------------------- | 1 | 1 | ... | | 2 | 2 | ... | | 3 | 2 | ... | | 4 | 1 | ... | ---------------------------
Create a virtual table (a/k/a subquery) with the lowest numerical order ID for each customer. 为每个客户创建具有最低数字订单ID的虚拟表(a / k / a子查询)。
SELECT customer_id, min(order_id)
FROM orders
GROUP BY customer_id
Then join that table with the customer table, like so. 然后将该表与客户表连接起来,就像这样。
SELECT C.customer_id, firstorder.order_id
FROM CUSTOMERS as C
LEFT JOIN (
SELECT customer_id, min(order_id)
FROM orders
GROUP BY customer_id
) AS firstorder ON c.customer_id = firstorder.customer_id
Try this 尝试这个
Select customer.*,Order.OrderNo As EarilerORderNo
From Customers Left Join
(Select customer_id,orderid from orders order by customer_id,orderid desc) As Orders
ON Customers.Id=Orders.OrderID
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