MySQL 选择类别和子类别（如果有产品）

Question

我正在尝试进行查询以解决此问题：

如果主类别包含产品或子类别包含产品，请选择主类别

问题在于它没有选择包含产品的子类别

SELECT Category.id, Category.name, Category.description, Category.image
FROM categories_table as Category
JOIN products_table as Product
WHERE Category.subcategory = 0 AND Product.category = Category.id    
    OR Category.id IN
    (
        SELECT SubProduct.categorie
        FROM kosBonusShop_regels AS SubProduct
        WHERE SubProduct.category = Category.subcategory
            AND Product.category = Category.id   
        GROUP BY Product.category
    )
GROUP BY Product.category


Product #1                               Category #1
id             | 1                       id          |  1
category       | 2 (Pencils)             subcategory |  0 (none)
description    | Pencil                  title       |  office supplies

Category #2
id          | 2
subcategory | 1 (office supplies)
title       | Pencils

产品铅笔应属于铅笔类别，铅笔类别应属于办公用品类别的子类别

办公用品类别也可以包含产品

Answer 1

在使用这样的子查询时，您应该使用 IN 关键字而不是等号。此外，在您的情况下，最好使用 JOIN 。试试这个：

SELECT Category.id, Category.name, Category.description, Category.image
FROM categories_table as Category
LEFT JOIN products_table as Product ON Product.category = Category.id
WHERE (Category.subcategory = 0 AND NOT ISNULL(Product.id))
    OR Category.id IN
    (
        SELECT SubProduct.categorie
        FROM kosBonusShop_regels AS SubProduct
        WHERE SubProduct.category = Category.subcategory
            AND Product.category = Category.id   
        GROUP BY Product.category
    )
GROUP BY Product.category