MySQL查询冻结

Question

我有以下查询

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') 

，旨在使我得到我的范围，或者从订单信息，优惠卡的用户订购的产品。当我第一次写它时，它似乎工作正常，但最近我被告知它冻结了，我不知道为什么。我试着玩一下它，似乎当我添加日期范围，或者甚至只是单一的日期搜索条件时，它会冻结（可以在PHPMyAdmin中永久显示'Loading'弹出窗口）;除此之外，执行大约需要1秒。

Here's what EXLAIN gives me.

Answer 1

好吧，显然抛出内加入了Discount_cards并用WHERE替代它修复了这个问题：

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') 

我不知道为什么这样做，冻结，虽然发生了，解释将不胜感激。