问题描述

我编写了一个查询，返回与 Customers 和 Salespeoeple 相关联的行.

I've written a query returning rows associating Customers and Salespeoeple.

请注意，该查询连接了多个数据库表.请注意，并非所有客户都有销售人员.

Note that the query joins several database tables. And note that not all customers have a salesperson.

c_id     c_name   s_id   s_name
  24  microsoft      1     mike
  27        sun      1     mike
  42      apple      2     bill
  44     oracle      1     mike
  47        sgi      1     mike
  58       ebay      2     bill
  61     paypal      3      joe
  65     redhat      1     mike

我的数据库中还有一个表(称为invoices)，如下所示.

I also have a single table (called invoices) in my database that looks like this.

i_id   c_id   c_name   s_id   s_name
7208     22   toyota   NULL     NULL
7209     23     ford   NULL     NULL
7210     27      sun   NULL     NULL
7211     42    apple   NULL     NULL
7212     12   nissan   NULL     NULL
7213     15       gm   NULL     NULL
7214     61   paypal   NULL     NULL

如何在 MySQL 中使用 UPDATE 使我的发票表如下表所示?

How can I use UPDATE in MySQL to make my invoices table look like the table below?

i_id   c_id   c_name   s_id   s_name
7208     22   toyota   NULL     NULL
7209     23     ford   NULL     NULL
7210     27      sun      1     mike
7211     42    apple      2     bill
7212     12   nissan   NULL     NULL
7213     15       gm   NULL     NULL
7214     61   paypal      3      joe

也就是说，我如何更新我的发票表以包含正确的 salesperson_id 和 salesperson_name，如果存在这种关系?

That is to say, how can I update my invoice table to include the correct salesperson_id and salesperson_name, where that relationship exists?

请注意，如果存在客户/销售人员关系，则该客户的所有发票都应有销售人员与之关联，前提是该客户有销售人员.

Note that where a Customer/Salesperson relationship exists, all invoices for that customer should have the salesperson associated with it, if there is a salesperson for that customer.

非常感谢 :-)

推荐答案

使用子查询

最广泛支持的选项

Using subqueries

Most widely supported option

UPDATE INVOICES
   SET s_id = (SELECT cs.s_id
                 FROM CUSTOMERS_AND_SALES cs
                WHERE cs.c_id = INVOICES.c_id),
       s_name = (SELECT cs.s_name
                   FROM CUSTOMERS_AND_SALES cs
                  WHERE cs.c_id = INVOICES.c_id)
 WHERE INVOICES.c_id IN (SELECT cs.s_id
                           FROM CUSTOMERS_AND_SALES cs)

使用 JOIN

UPDATE INVOICES
  JOIN CUSTOMERS_AND_SALES cs ON cs.c_id = INVOICES.c_id
   SET s_id = cs.s_id,
       s_name = cs.s_name

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