mysql join 三个表联接查询实例详解
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2022-04-07 11:51:01
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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: 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
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 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。