SQL帮助 - 计算两个表中的行

Question

我有2张桌子：产品＆amp;类

我正在尝试编写sql来计算每个类别的产品数量。到目前为止，我有这个：

SELECT `name`, count(*) as `size`
FROM products
INNER JOIN category ON category.`id` = products.`categoryID`
GROUP BY category.`name`

这将返回每个类别名称的列表以及该类别的产品数量。但是，它不会列出包含0个产品的类别。我该如何解决这个问题？

Answer 1

使用正确的联接。

SELECT `name`, count(*) as `size`
FROM products
RIGHT JOIN category ON category.`id` = products.`categoryID`
GROUP BY category.`name`

Answer 2

尝试：

SELECT `name`, count(products.id) as `size`
FROM category
LEFT JOIN products ON category.`id` = products.`categoryID`
GROUP BY category.`name`