MySQL 一对多查询

Posted 2021-01-31 xiaofengfree

group_concat
简单来说，这个函数的作用就是连接多个字段

数据表
首先我们先建立两个表

 1 CREATE TABLE `student` (
 2   `id` int(11) NOT NULL AUTO_INCREMENT,
 3   `name` char(10) NOT NULL,
 4   PRIMARY KEY (`id`)
 5 ) ENGINE=MyISAM AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
 6 
 7 -- ----------------------------
 8 -- Records of student
 9 -- ----------------------------
10 INSERT INTO `student` VALUES (‘1‘, ‘tom‘);
11 INSERT INTO `student` VALUES (‘2‘, ‘jerry‘);
12 
13 CREATE TABLE `course` (
14   `id` int(11) NOT NULL AUTO_INCREMENT,
15   `s_id` int(11) NOT NULL,
16   `c_name` char(10) NOT NULL,
17   PRIMARY KEY (`id`)
18 ) ENGINE=MyISAM AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
19 
20 -- ----------------------------
21 -- Records of course
22 -- ----------------------------
23 INSERT INTO `course` VALUES (‘1‘, ‘1‘, ‘语文‘);
24 INSERT INTO `course` VALUES (‘2‘, ‘1‘, ‘数学‘);
25 INSERT INTO `course` VALUES (‘3‘, ‘2‘, ‘英语‘);
26 INSERT INTO `course` VALUES (‘4‘, ‘2‘, ‘体育‘);
27 INSERT INTO `course` VALUES (‘5‘, ‘2‘, ‘美术‘);

View Code

下面用 group_concat 函数查询

1 SELECT S.`NAME`,(SELECT GROUP_CONCAT(COURSE.C_NAME) FROM COURSE WHERE COURSE.S_ID = S.ID) FROM STUDENT AS S;

View Code