首先创建三个表;分别为Books表、Authors表和AuthorBook表。 mysql创建表代码如下: mysql> CREATE TABLE Books( -> BookID SMALLINT NOT NULL PRIMARY KEY, -> BookTitle VARCHAR(60) NOT NULL, -> Copyright YEAR NOT NULL -> ) -> ENGINE=INNODB;Query OK, 0 rows affected (0.03 sec)mysql> CREATE TABLE Authors( -> AuthID SMALLINT NOT NULL PRIMARY KEY, -> AuthFN VARCHAR(20), -> AuthMN VARCHAR(20), -> AuthLN VARCHAR(20) -> ) -> ENGINE=INNODB;Query OK, 0 rows affected (0.06 sec)mysql> CREATE TABLE AuthorBook( -> AuthID SMALLINT NOT NULL, -> BookID SMALLINT NOT NULL, -> PRIMARY KEY (AuthID, BookID), -> FOREIGN KEY (AuthID) REFERENCES Authors (AuthID), -> FOREIGN KEY (BookID) REFERENCES Books (BookID) -> ) -> ENGINE=INNODB;Query OK, 0 rows affected (0.03 sec)
然后分别向这三个表中插入一些数据: mysql> INSERT INTO Books VALUES (12786, 'Java', 1934), -> (13331, 'MySQL', 1919), -> (14356, 'PHP', 1966), -> (15729, 'PERL', 1932), -> (16284, 'Oracle', 1996), -> (17695, 'Pl/SQL', 1980), -> (19264, 'JavaScript', 1992), -> (19354, 'www.java2s.com', 1993);Query OK, 8 rows affected (0.03 sec)Records: 8 Duplicates: 0 Warnings: 0mysql> INSERT INTO Authors VALUES (1006, 'H', 'S.', 'T'), -> (1007, 'J', 'C', 'O'), -> (1008, 'B', NULL, 'E'), -> (1009, 'R', 'M', 'R'), -> (1010, 'J', 'K', 'T'), -> (1011, 'J', 'G.', 'N'), -> (1012, 'A', NULL, 'P'), -> (1013, 'A', NULL, 'W'), -> (1014, 'N', NULL, 'A');Query OK, 9 rows affected (0.03 sec)Records: 9 Duplicates: 0 Warnings: 0mysql> INSERT INTO AuthorBook VALUES (1006, 14356), -> (1008, 15729), -> (1009, 12786), -> (1010, 17695), -> (1011, 15729), -> (1012, 19264), -> (1012, 19354), -> (1014, 16284);Query OK, 8 rows affected (0.05 sec)Records: 8 Duplicates: 0 Warnings: 0
现在开始对这三个表进行联合查询操作。 需求:获取所有书籍的名称、作者和发布时间。 下面请看mysql使用join如何实现: mysql> SELECT BookTitle, Copyright, CONCAT_WS(' ', AuthFN, AuthMN, AuthLN) AS Author -> FROM Books JOIN AuthorBook USING (BookID) -> JOIN Authors USING (AuthID) -> WHERE Copyright<1980 -> ORDER BY BookTitle;+-----------+-----------+--------+| BookTitle | Copyright | Author |+-----------+-----------+--------+| Java | 1934 | R M R || PERL | 1932 | B E || PERL | 1932 | J G. N || PHP | 1966 | H S. T |+-----------+-----------+--------+4 rows in set (0.00 sec)
大家可以自己把mysql代码粘贴过去在自己的电脑上运行一下,多动手多思考应该可以理解。 |