The content of this article is about the code example of MySQL implementing one-to-many query. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.
What we want to implement this time is a one-to-many query, which is implemented using MySQL’s group_concat function.
group_concat
Simply put, the function of this function is to connect multiple fields. For a detailed explanation of the function, please see this article.
Data table
First we create two tables
CREATE TABLE `student` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` char(10) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES ('1', 'tom');
INSERT INTO `student` VALUES ('2', 'jerry');
CREATE TABLE `course` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`s_id` int(11) NOT NULL,
`c_name` char(10) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
-- ----------------------------
-- Records of course
-- ----------------------------
INSERT INTO `course` VALUES ('1', '1', '语文');
INSERT INTO `course` VALUES ('2', '1', '数学');
INSERT INTO `course` VALUES ('3', '2', '英语');
INSERT INTO `course` VALUES ('4', '2', '体育');
INSERT INTO `course` VALUES ('5', '2', '美术');
If we use the usual SQL query
SELECT s.`name`,c.`c_name` FROM student AS s LEFT JOIN course AS c ON c.s_id = s.id;
The result of the query is
Use the group_concat function query
SELECT s.`name`,(SELECT group_concat(course.c_name) FROM course WHERE course.s_id = s.id) FROM student AS s;
to query at this time the result of
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