使用特定標準從兩個表中提取數據

Question

我正在做的是：提取數據以向用戶顯示產品，以便他/她可以評估產品。使用下面的查詢可以正常工作。

$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"; 

現在我想問的是：如何僅顯示用戶尚未評分的產品。一旦用戶對產品進行評級後，該產品不應再由該用戶的查詢獲取。

我有3個表

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) 

，並希望從2個表

獲取數據

table_users, table_products 

數據中獲取

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

如何爲這個任務設置查詢一個具體的used_id

感謝您的時間和幫助:)

Answer 1

你可以加入收視率表和統計收視率的數量然後檢查它在where子句中，這樣的事情（未經測試）：

$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

有是多種方式，你需要連接表，分組和使用條款，請參考圖像。

Answer 3

使用此查詢

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