GROUP_CONCAT 分组连接

准备的数据示例

CREATE TABLE `students` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  `className` varchar(100) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `sex` int(11) DEFAULT NULL COMMENT '性别 1 男 2女',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=12 DEFAULT CHARSET=utf8mb4;

INSERT INTO db1.students
(id, name, className, age, sex)
VALUES(1, '王晓宇', '六(1)班', 12, 2);
INSERT INTO db1.students
(id, name, className, age, sex)
VALUES(2, '杜明月', '六(1)班', 11, 2);
INSERT INTO db1.students
(id, name, className, age, sex)
VALUES(8, '李慕然', '六(1)班', 11, 1);
INSERT INTO db1.students
(id, name, className, age, sex)
VALUES(9, '马曦铭', '六(1)班', 11, 1);
INSERT INTO db1.students
(id, name, className, age, sex)
VALUES(10, '王秋白', '六(2)班', 11, 1);
INSERT INTO db1.students
(id, name, className, age, sex)
VALUES(11, '刘胜明', '六(3)班', 11, NULL);

GROUP_CANCAT 的使用

分班级列出名单

select className ,GROUP_CONCAT(name)  from students s  group by s.className 

分班级列出名单并包含显示性别

由于存在用于没有填写性别，所以这里不能直接CONCAT，否则就像下面的情况，存在空值的行连接被丢弃

select className ,GROUP_CONCAT(name,'(',sex,')')  from students s  group by s.className

组合IFNULL

我们可以使用IFNULL将其转换

select className ,GROUP_CONCAT(name,'(',IFNULL(sex,0),')')  from students s  group by s.className

组合IF

将其转换为中文性别

select className ,GROUP_CONCAT(name,'(',IF(sex=1,'男',IF(sex=2,'女','未填写')),')')  from students s  group by s.className

组合case when

select className ,GROUP_CONCAT(name,'(',CASE WHEN sex is null THEN '未填写' WHEN sex=1 THEN '男' WHEN sex =2 THEN '女' END  ,')') 
from students s  group by s.className