未能比我承认的更长时间地破解这个。
我不认为这可能是一个不寻常的问题 - 当然mapping table troubles在SQL领域只有一打 - 所以我只会问,希望其他人可以从我的无知中受益。 / p>
我正在尝试将五个表拉在一起,以显示连接到主类别和子类别的产品。 我想要显示的是产品表中的信息。
表格如下:
**products**
product_id (PK) | [other columns with product information]
**categories**
category_id (PK) | category_name
**sub_categories**
sub_category_id (PK) | sub_category_name
**products_and_categories**
pc_rel_id (PK) | pc_product_id (FK - products.product_id) | pc_category_id (FK - categories.category_id)
**products_and_sub_categories**
psc_rel_id (PK) | psc_product_id (FK - products.product_id) | psc_sub_category_id (FK - sub_categories.sub_category_id)
到目前为止,我毫无结果的尝试包括:
$getSCatProds = new QueryClass();
$catSubArray['queryCategory'] = 'main category name';
$catSubArray['querySubCategory'] = 'sub category name';
//PDO fetchAll(PDO::FETCH_ASSOC)
$resultArray = $getSCatProds->fetchAllQuery("SELECT product_id FROM products
INNER JOIN (products_and_categories, products_and_sub_categories)
ON (products_and_categories.pc_product_id=products.product_id
AND products_and_sub_categories.psc_product_id=products.product_id)
INNER JOIN (categories, sub_categories)
ON (categories.category_id = products_and_categories.pc_category_id
AND sub_categories.sub_category_id = products_and_sub_categories.psc_sub_category_id)
WHERE categories.category_name = :queryCategory
AND sub_categories.sub_category_name = :querySubCategory", $catSubArray);
print_r($resultArray); //returns an empty array
和
//Query method and sent information same as in the above query
$resultArray = $getSCatProds->fetchAllQuery("SELECT product_id FROM products
INNER JOIN (products_and_categories, products_and_sub_categories, categories, sub_categories)
ON (products_and_categories.pc_product_id=products.product_id
AND products_and_sub_categories.psc_product_id=products.product_id)
WHERE categories.category_name = :queryCategory
AND sub_categories.sub_category_name = :querySubCategory", $catSubArray);
print_r($resultArray);
//returns a stupendous number of product_id:s, 2030 of them to be exact.
//There are 2075 items in the products table ...
请给我可怜的小伙伴找一个正确的问题。
谢谢。
答案 0 :(得分:2)
您需要为每个表单独进行连接。
SELECT p.product_id
FROM products AS p
JOIN products_and_categories AS pc ON p.product_id = pc.pc_product_id
JOIN categories AS c ON pc.pc_category_id = c.category_id
JOIN products_and_subcategories AS psc ON p.product_id = psc.psc_product_id
JOIN sub_categories AS sc ON psc.psc_sub_category_id = sc.sub_category_id
WHERE c.category_name = :queryCategory
AND sc.sub_category_name = :querySubCategory