关于内、外链接的示例

时间：2011-04-30 来源：[守岁]

表如下

SET NOCOUNT ON;
USE tempdb;

IF OBJECT_ID('dbo.Orders') IS NOT NULL DROP TABLE dbo.Orders;
IF OBJECT_ID('dbo.Customers') IS NOT NULL DROP TABLE dbo.Customers;
GO

CREATE TABLE dbo.Customers
(
  customerid  CHAR(5)     NOT NULL PRIMARY KEY,
  city        VARCHAR(10) NOT NULL
);

CREATE TABLE dbo.Orders
(
  orderid    INT     NOT NULL PRIMARY KEY,
  customerid CHAR(5)     NULL REFERENCES Customers(customerid)
);
GO

INSERT INTO dbo.Customers(customerid, city) VALUES('FISSA', 'Madrid');
INSERT INTO dbo.Customers(customerid, city) VALUES('FRNDO', 'Madrid');
INSERT INTO dbo.Customers(customerid, city) VALUES('KRLOS', 'Madrid');
INSERT INTO dbo.Customers(customerid, city) VALUES('MRPHS', 'Zion');

INSERT INTO dbo.Orders(orderid, customerid) VALUES(1, 'FRNDO');
INSERT INTO dbo.Orders(orderid, customerid) VALUES(2, 'FRNDO');
INSERT INTO dbo.Orders(orderid, customerid) VALUES(3, 'KRLOS');
INSERT INTO dbo.Orders(orderid, customerid) VALUES(4, 'KRLOS');
INSERT INTO dbo.Orders(orderid, customerid) VALUES(5, 'KRLOS');
INSERT INTO dbo.Orders(orderid, customerid) VALUES(6, 'MRPHS');
INSERT INTO dbo.Orders(orderid, customerid) VALUES(7, NULL);

这2张表可以很清晰的看出外链接

SELECT * FROM Customers JOIN Orders ON Customers.customerid = Orders.customerid
SELECT * FROM Customers LEFT OUTER JOIN Orders ON Customers.customerid = Orders.customerid
SELECT * FROM Customers RIGHT OUTER JOIN Orders ON Customers.customerid = Orders.customerid
SELECT * FROM Customers FULL OUTER JOIN Orders ON Customers.customerid = Orders.customerid

其结果如下

customerid city       orderid     customerid
---------- ---------- ----------- ----------
FRNDO      Madrid     1           FRNDO
FRNDO      Madrid     2           FRNDO
KRLOS      Madrid     3           KRLOS
KRLOS      Madrid     4           KRLOS
KRLOS      Madrid     5           KRLOS
MRPHS      Zion       6           MRPHS

(6 行受影响)

customerid city       orderid     customerid
---------- ---------- ----------- ----------
FISSA      Madrid     NULL        NULL
FRNDO      Madrid     1           FRNDO
FRNDO      Madrid     2           FRNDO
KRLOS      Madrid     3           KRLOS
KRLOS      Madrid     4           KRLOS
KRLOS      Madrid     5           KRLOS
MRPHS      Zion       6           MRPHS

(7 行受影响)