我在这里和谷歌中没有找到任何 MYSQL 多对多关系示例。我正在寻找的是一个非常简单的示例,其中 php+mysql 显示数据库的结果。有人可以写一个非常简单的例子吗?
示例场景:大学的学生和课程。一个特定的学生可能会参加多门课程,当然一门课程通常会有很多学生。
示例表,简单设计:
CREATE TABLE `Student` (
`StudentID` INT UNSIGNED NOT NULL AUTO_INCREMENT,
`FirstName` VARCHAR(25),
`LastName` VARCHAR(25) NOT NULL,
PRIMARY KEY (`StudentID`)
) ENGINE=INNODB CHARACTER SET utf8 COLLATE utf8_general_ci
CREATE TABLE `Course` (
`CourseID` SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
`Code` VARCHAR(10) CHARACTER SET ascii COLLATE ascii_general_ci NOT NULL,
`Name` VARCHAR(100) NOT NULL,
PRIMARY KEY (`CourseID`)
) ENGINE=INNODB CHARACTER SET utf8 COLLATE utf8_general_ci
CREATE TABLE `CourseMembership` (
`Student` INT UNSIGNED NOT NULL,
`Course` SMALLINT UNSIGNED NOT NULL,
PRIMARY KEY (`Student`, `Course`),
CONSTRAINT `Constr_CourseMembership_Student_fk`
FOREIGN KEY `Student_fk` (`Student`) REFERENCES `Student` (`StudentID`)
ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `Constr_CourseMembership_Course_fk`
FOREIGN KEY `Course_fk` (`Course`) REFERENCES `Course` (`CourseID`)
ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=INNODB CHARACTER SET ascii COLLATE ascii_general_ci
查找注册课程的所有学生:
SELECT
`Student`.*
FROM
`Student`
JOIN `CourseMembership` ON `Student`.`StudentID` = `CourseMembership`.`Student`
WHERE
`CourseMembership`.`Course` = 1234
查找给定学生修读的所有课程:
SELECT
`Course`.*
FROM
`Course`
JOIN `CourseMembership` ON `Course`.`CourseID` = `CourseMembership`.`Course`
WHERE
`CourseMembership`.`Student` = 5678
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