首先我们创建数据库表：

CREATE TABLE `t_demo` (
  `id` int(32) NOT NULL,
  `name` varchar(255) DEFAULT NULL,
  `age` int(2) DEFAULT NULL,
  `num` int(3) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

插入数据：

INSERT INTO `t_demo` VALUES (‘1‘, ‘张三‘, ‘21‘, ‘69‘);
INSERT INTO `t_demo` VALUES (‘2‘, ‘李四‘, ‘22‘, ‘98‘);
INSERT INTO `t_demo` VALUES (‘3‘, ‘王五‘, ‘20‘, ‘54‘);
INSERT INTO `t_demo` VALUES (‘4‘, ‘赵甜‘, ‘22‘, ‘80‘);

MySQL case when 用法

SELECT
    *,
CASE
    WHEN t.num >= 85 THEN
        ‘优秀‘
    WHEN t.num < 90 AND t.num>= 60 THEN
        ‘一般‘
    ELSE
        ‘不及格‘
    END AS level
FROM
    t_demo t;

查询结构：

?

原文地址：https://www.cnblogs.com/zhaixingzhu/p/12569288.html