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');
Instance
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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