使用特定条件

Question

我正在做的是：获取数据以向用户显示产品，以便他/她可以对产品进行评级。使用以下查询可以正常工作。

$query = "  SELECT      table_products.product_name, 
                        table_products.product_expiry, 
                        table_users.name,
                        table_users.email

            FROM table_products
            INNER JOIN table_users ON table_users.user_id = table_products.user_id 
            ORDER BY table_users.id DESC";

现在我想问的是：如何仅显示用户尚未评级的产品。用户对产品评分后，该用户的查询不应再次提取该产品。

我有3张桌子

table_users (user_id, name, email)

table_products (product id_, user_id, product_name, product_expiry)

table_rating (rating_id, user_id, product_id, rating)

我想从2个表中获取数据

table_users, table_products

要提取的数据

table_users.name, 
table_users.email, 
table_products.product_name, 
table_products.product_expiry

如何为特定user_id设置此任务的查询？

感谢您的时间和帮助：）

Answer 1

您可以加入评级表并计算评分数量，然后在where子句中查看，如下所示（未经测试）：

$query = "SELECT
table_products.product_name, 
table_products.product_expiry, 
table_users.name,
table_users.email,
count(table_rating.id) as ratings

FROM table_products
INNER JOIN table_users ON table_users.user_id = table_products.user_id 
left join table_rating ON table_rating.product_id = table_products.id

where ratings = 0
ORDER BY table_users.id DESC";

Answer 2

有多种方式，你需要连接表，分组和使用having子句，请参考图像。

Answer 3

使用此查询

SELECT      table_products.product_name, 
                        table_products.product_expiry, 
                        table_users.name,
                        table_users.email

            FROM table_products
            INNER JOIN table_users ON table_users.user_id = table_products.user_id 
            LEFT JOIN table_rating on table_products.product_id=table_rating.product_id
            WHERE table_rating.product_id IS NULL
            ORDER BY table_users.id DESC

Answer 4

SELECT      
table_products.product_name, 
table_products.product_expiry, 
table_users.name,
table_users.email

FROM table_products
INNER JOIN table_users ON table_users.user_id = table_products.user_id

LEFT JOIN table_rating ON table_products.user_id = table_rating.user_id 
AND table_products.product_id = table_rating.product_id

WHERE table_rating.product_id IS NULL

ORDER BY table_users.user_id DESC