mySQL 内部连接多个表

Question

如果我发布这行代码:

SELECT Cheese.Chesse_Name
FROM Customer
INNER JOIN Customer ON Customer.Customer_ID = Orders.Customer_ID
INNER JOIN Orders ON Orders.Orders_ID = OrderSandwich.Orders_ID
INNER JOIN OrderSandwich ON OrderSandwich.Sandwich_ID = Sandwich.Sandwich_ID
INNER JOIN Sandwich ON Sandwich.Cheese_ID = Cheese.Cheese_ID
WHERE Customer.CustomerID = 1;

我从数据库中得到的只是一个错误

Fehler

SQL-Befehl: Dokumentation

SELECT Cheese.Chesse_Name
FROM Customer
INNER JOIN Customer ON Customer.Customer_ID = Orders.Customer_ID
INNER JOIN Orders ON Orders.Orders_ID = OrderSandwich.Orders_ID
INNER JOIN OrderSandwich ON OrderSandwich.Sandwich_ID = Sandwich.Sandwich_ID
INNER JOIN Sandwich ON Sandwich.Cheese_ID = Cheese.Cheese_ID
WHERE Customer.CustomerID = 1
 LIMIT 0, 25 

MySQL meldet: Dokumentation
#1066 - Not unique table/alias: 'Customer' 

我现在正在尝试这个几个小时而不是说空洞日。

这是数据库图:

如果有人马上看到我犯的错误，我将非常感激

Answer 1

您正在尝试将 Customer 表与其自身连接起来。重新组织您的 JOIN 查询，如下所示。

SELECT Cheese.Cheese_Name
FROM Customer
INNER JOIN Orders ON Customer.Customer_ID = Orders.Customer_ID
INNER JOIN OrderSandwich ON Orders.Orders_ID = OrderSandwich.Orders_ID
INNER JOIN Sandwich ON OrderSandwich.Sandwich_ID = Sandwich.Sandwich_ID
INNER JOIN Cheese ON Sandwich.Cheese_ID = Cheese.Cheese_ID
WHERE Customer.Customer_ID = 1;

请记住，您正在调用 JOIN 语句，将提到的表与上面的表连接起来。例如，如果您调用

Customer
INNER JOIN Orders ON Customer.Customer_ID = Orders.Customer_ID

您正在加入 Customer 表和 Orders 表。无需两次提及 Customer 表。