使用联接的MySQL查询搜索

Question

我有以下表格：

products table
-------------
id
name
...

categories table
----------------
id
name

product_categories table
------------------------
product_id
category_id

product_ratings
---------------
product_id
user_id
rating (1 to 5 INT)

如何选择按类别（名称或ID）选择（搜索）产品和等级（平均），并按标题或等级排序。

我已经尝试了一些查询，但是即时通讯在如何联接表以及如何使用where子句方面遇到了一些麻烦

Answer 1

你的意思是那样吗？

select
    products.name, categories.name, product_ratings.rating
from products
join product_categories on products.id = product_categories.product_id
join categories on  categories.id = product_categories.category_id
join product_ratings on product_ratings.product_id = products.id
where
    categories.name = 'CATEGORY NAME'
order by
    product_ratings.rating

Answer 2

select p.name, r.rating
from products as p
inner join product_ratings as  r on p.id = r.product_id
inner join categories as c on c.id = pc.category_id
inner join product_categories as pc = pc.product_id = p.id
where c.name = 'search_name'
order by r.rating;

Answer 3

方法1

按产品和用户ID评分

SELECT
P.name, PR.user_id , IFNULL(PR.rating,0) as rating
FROM products P
JOIN product_categories PC ON P.id = PC.product_id
JOIN categories C ON C.id = PC.category_id
JOIN product_ratings PR ON PR.product_id = P.id
WHERE C.name = 'Category A'
ORDER BY P.name

请参阅http://sqlfiddle.com/#!9/014af/6

方法二

按产品编号评分

不同的用户会对同一产品进行评分，因此我们必须考虑每种产品的平均评分。

SELECT
P.name, GROUP_CONCAT(PR.user_id) as user_ids, AVG(IFNULL(PR.rating,0)) as rating
FROM products P
JOIN product_categories PC ON P.id = PC.product_id
JOIN categories C ON C.id = PC.category_id
JOIN product_ratings PR ON PR.product_id = P.id
WHERE C.name = 'Category A'
GROUP BY P.id 
ORDER BY P.name

请参阅http://sqlfiddle.com/#!9/014af/7