SQL笛卡爾或交叉連接

笛卡爾連接或交叉連接從兩個或多個連接表返回笛卡爾乘積的記錄。因此，它相當於一個內部聯接，其中聯接條件始終計算爲真或者聯接條件是從語句中空缺。

語法

笛卡爾連接的基本語法如下：

SELECT table1.column1, table2.column2... FROM table1, table2 [, table3 ]

例子：

考慮下面的兩個表中，(a)CUSTOMERS表如下：

+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+

（b）另一個ORDERS 表如下：

+-----+---------------------+-------------+--------+ |OID | DATE | CUSTOMER_ID | AMOUNT | +-----+---------------------+-------------+--------+ | 102 | 2009-10-08 00:00:00 | 3 | 3000 | | 100 | 2009-10-08 00:00:00 | 3 | 1500 | | 101 | 2009-11-20 00:00:00 | 2 | 1560 | | 103 | 2008-05-20 00:00:00 | 4 | 2060 | +-----+---------------------+-------------+--------+

現在，讓我們使用笛卡爾連接在這兩個表如下：

SQL> SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS, ORDERS;

這將產生以下結果:

+----+----------+--------+---------------------+ | ID | NAME | AMOUNT | DATE | +----+----------+--------+---------------------+ | 1 | Ramesh | 3000 | 2009-10-08 00:00:00 | | 1 | Ramesh | 1500 | 2009-10-08 00:00:00 | | 1 | Ramesh | 1560 | 2009-11-20 00:00:00 | | 1 | Ramesh | 2060 | 2008-05-20 00:00:00 | | 2 | Khilan | 3000 | 2009-10-08 00:00:00 | | 2 | Khilan | 1500 | 2009-10-08 00:00:00 | | 2 | Khilan | 1560 | 2009-11-20 00:00:00 | | 2 | Khilan | 2060 | 2008-05-20 00:00:00 | | 3 | kaushik | 3000 | 2009-10-08 00:00:00 | | 3 | kaushik | 1500 | 2009-10-08 00:00:00 | | 3 | kaushik | 1560 | 2009-11-20 00:00:00 | | 3 | kaushik | 2060 | 2008-05-20 00:00:00 | | 4 | Chaitali | 3000 | 2009-10-08 00:00:00 | | 4 | Chaitali | 1500 | 2009-10-08 00:00:00 | | 4 | Chaitali | 1560 | 2009-11-20 00:00:00 | | 4 | Chaitali | 2060 | 2008-05-20 00:00:00 | | 5 | Hardik | 3000 | 2009-10-08 00:00:00 | | 5 | Hardik | 1500 | 2009-10-08 00:00:00 | | 5 | Hardik | 1560 | 2009-11-20 00:00:00 | | 5 | Hardik | 2060 | 2008-05-20 00:00:00 | | 6 | Komal | 3000 | 2009-10-08 00:00:00 | | 6 | Komal | 1500 | 2009-10-08 00:00:00 | | 6 | Komal | 1560 | 2009-11-20 00:00:00 | | 6 | Komal | 2060 | 2008-05-20 00:00:00 | | 7 | Muffy | 3000 | 2009-10-08 00:00:00 | | 7 | Muffy | 1500 | 2009-10-08 00:00:00 | | 7 | Muffy | 1560 | 2009-11-20 00:00:00 | | 7 | Muffy | 2060 | 2008-05-20 00:00:00 | +----+----------+--------+---------------------+