SQL Join聯(lián)接子句用于在兩個(gè)或更多在數(shù)據(jù)庫中的表的記錄組合。JOIN是通過使用從兩個(gè)表字段共通的值組合連接起來。
考慮下面的兩個(gè)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(gè)表的命令如下:
+-----+---------------------+-------------+--------+ |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(xiàn)在,讓我們在SELECT語句中聯(lián)接這兩個(gè)表如下:
SQL> SELECT ID, NAME, AGE, AMOUNT FROM CUSTOMERS, ORDERS WHERE CUSTOMERS.ID = ORDERS.CUSTOMER_ID;
這將產(chǎn)生以下結(jié)果:
+----+----------+-----+--------+ | ID | NAME | AGE | AMOUNT | +----+----------+-----+--------+ | 3 | kaushik | 23 | 3000 | | 3 | kaushik | 23 | 1500 | | 2 | Khilan | 25 | 1560 | | 4 | Chaitali | 25 | 2060 | +----+----------+-----+--------+
在這里,值得注意的是,在WHERE子句中加Join。幾家運(yùn)算符可以用來連接表,如=, <, >, <>, <=, >=, !=, BETWEEN, LIKE, 和 NOT; 他們都可以被用來連接表。然而,最常見的運(yùn)算符是等于符號。
在SQL連接有不同類型可用: