Mysql 当存在ID关联时，如何从多个表中获取行

我使用的是MySql，我的数据库结构如下所示

Table: product
Structure: product_id - manufacturer_id
Example #1: 30 - 9
Example #2: 31 - 0

表中没有制造商id 0

Table: manufacturer
Structure: manufacturer_id - name
Example #1: 9 - Canon

因此，我尝试使用下面的代码，但产品ID 9未列出

SELECT product.product_id, IF(product.manufacturer_id > 0, manufacturer.name, 'Unknown') AS manufacturer FROM product, manufacturer WHERE product.manufacturer_id=manufacturer.manufacturer_id ORDER BY product.product_id ASC

我需要得到如下输出：

Structure: product_id - manufacturer
Output:
    30 - Canon
    31 - Unknown

我搜索了很多，尝试了很多不同的方法，但没有成功。 提前感谢。

您应该像这样尝试左键连接：

SELECT product.id, ISNULL(manufacturer.name, 'Unknown name') FROM Product INNER JOIN manufacturer ON(Product.manufacturer_id = manufacturer.manufacturer_id)

SELECT op.product_id, IFNULL(om.name, 'Unknown')
FROM oc_product op
LEFT JOIN oc_manufacturer om ON op.product_id = om.manufacturer_id
ORDER BY op.product_id ASC

---

在测试了两个答案后，我发现这一个有效：

SELECT product.product_id, IFNULL(manufacturer.name, 'Unknown') FROM product LEFT JOIN manufacturer ON product.manufacturer_id = manufacturer.manufacturer_id ORDER BY product.product_id ASC

谢谢你们的帮助

SELECT product.product_id, IFNULL(manufacturer.name, 'Unknown') FROM product LEFT JOIN manufacturer ON product.manufacturer_id = manufacturer.manufacturer_id ORDER BY product.product_id ASC