Home >Database >Mysql Tutorial >mysql join 三个表联接查询实例详解
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:
<code class="language-sql">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)</code>
然后分别向这三个表中插入一些数据:
<code class="language-sql">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: 0 mysql> 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: 0 mysql> 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</code>
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:
<code class="language-sql">mysql> SELECT BookTitle, Copyright, CONCAT_WS(' ', AuthFN, AuthMN, AuthLN) AS Author -> FROM Books JOIN AuthorBook USING (BookID) -> JOIN Authors USING (AuthID) -> WHERE Copyright 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)</code>
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。