Question

我正在使用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

表格中没有manufacturer_id 0.

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

因此，我尝试使用下面的代码，但未列出产品ID 9

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

Structure: product_id - manufacturer
Output:
    30 - Canon

我需要得到像这样的输出：

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

我经常搜索并尝试以多种方式进行，但没有成功。提前谢谢。

Answer 1

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

Answer 2

你应该尝试LEFT JOIN这样：

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

Answer 3

在测试了两个答案之后，我发现这个答案有效：

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

感谢您的帮助。

如果存在ID关联，如何从多个表中获取行

3 个答案: