MySQL查詢凍結

Question

我有以下查詢

SELECT DISTINCT 
    Products.Product_name 
    FROM Order_details 
    INNER JOIN Products 
    ON Products.Product_codenumber = Order_details.Product_codenumber 
    INNER JOIN Orders 
    ON Order_details.Order_ID = Orders.Order_ID 
    INNER JOIN Customers 
    ON Orders.Customer_ID = Customers.Customer_ID 
    INNER JOIN Discount_cards 
    ON Discount_cards.Phone_number = Customers.Login 
    WHERE Orders.Status_ID = '5' 
    AND (DATE(Orders.Time) BETWEEN '$start_date' AND '$end_date') 

，旨在使我得到我的範圍，或者從訂單信息，優惠卡的用戶訂購的產品。當我第一次寫它時，它似乎工作正常，但最近我被告知它凍結了，我不知道爲什麼。我試着玩一下它，似乎當我添加日期範圍，或者甚至只是單一的日期搜索條件時，它會凍結（可以在PHPMyAdmin中永久顯示'Loading'彈出窗口）;除此之外，執行大約需要1秒。

Here's what EXLAIN gives me.

Answer 1

好吧，顯然拋出內加入了Discount_cards並用WHERE替代它修復了這個問題：

SELECT DISTINCT 
    Products.Product_name 
    FROM Order_details 
    INNER JOIN Products 
    ON Products.Product_codenumber = Order_details.Product_codenumber 
    INNER JOIN Orders 
    ON Order_details.Order_ID = Orders.Order_ID 
    INNER JOIN Customers 
    ON Orders.Customer_ID = Customers.Customer_ID 
    WHERE 
    Customers.Login IN (
     SELECT 
     Phone_number 
     FROM Discount_cards 
     ) 
    AND Orders.Status_ID = '5' 
    AND (DATE(Orders.Time) BETWEEN '$start_date' AND '$end_date') 

我不知道爲什麼這樣做，凍結，雖然發生了，解釋將不勝感激。