[英]SQL One-To-Many relationship
我是SQL
新手,我想在两个表之间创建One-To-Many
关系。 我使用以下查询创建了这两个表:
CREATE TABLE Customers
(
CustomerId INT NOT NULL AUTO_INCREMENT,
FirstName VARCHAR(255) NOT NULL,
LastName VARCHAR(255) NOT NULL,
Email VARCHAR(255) NOT NULL,
Address VARCHAR(255) NOT NULL,
PRIMARY KEY(CustomerId)
);
CREATE TABLE Orders
(
OrderId INT NOT NULL AUTO_INCREMENT,
Date DATE NOT NULL,
Quantity INT NOT NULL,
TotalDue FLOAT NOT NULL,
CustomerId INT NOT NULL,
PRIMARY KEY(OrderId),
FOREIGN KEY(CustomerId) REFERENCES Customers(CustomerId)
);
然而,即使我设置CustomerId
作为一个外键Orders
表,我仍然能够在添加行Orders
表与CustomerId
是不存在的Customers
表。 为什么会这样,如何在表之间创建真正的链接?
这是表的样子(从我的mysql
客户端复制/粘贴):
mysql> select * from Customers;
+------------+-----------+----------+-------------------+------------------------+
| CustomerId | FirstName | LastName | Email | Address |
+------------+-----------+----------+-------------------+------------------------+
| 1 | Jacks | James | james98@yahoo.com | Str. Moony, No. 9 |
| 2 | Mock | Grad | rrfuX@yahoo.com | Str. Mars, No. 91 |
| 3 | James | Geremy | gv@yahoo.com | Str. Monday, No. 12 |
| 4 | Joana | Joan | iiogn@yahoo.com | Str. Comete, No. 19 |
| 5 | Granicer | James | gtuawr@yahoo.com | Str. Sydney, No. 651 |
+------------+-----------+----------+-------------------+------------------------+
5 rows in set (0.00 sec)
mysql> select * from Orders;
+---------+------------+----------+----------+------------+
| OrderId | Date | Quantity | TotalDue | CustomerId |
+---------+------------+----------+----------+------------+
| 1 | 2014-01-09 | 10 | 340 | 3 |
| 2 | 2014-01-09 | 1 | 50 | 3 |
| 3 | 2014-01-09 | 11 | 55 | 5 |
| 4 | 2014-01-09 | 11 | 55 | 51 |
+---------+------------+----------+----------+------------+
4 rows in set (0.00 sec)
如您所见, OrderId
4包含一个CustomerId
51的客户,不在Customers
表中。
您需要设置存储引擎...将查询更改为...
CREATE TABLE Orders
(
OrderId INT NOT NULL AUTO_INCREMENT,
Date DATE NOT NULL,
Quantity INT NOT NULL,
TotalDue FLOAT NOT NULL,
CustomerId INT NOT NULL,
PRIMARY KEY(OrderId),
FOREIGN KEY(CustomerId) REFERENCES Customers(CustomerId)
)ENGINE=INNODB;
将InnoDB用于表引擎。
ALTER TABLE table_name ENGINE=InnoDB;
我放弃并开始使用MySQL的Web客户端...
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