MySQL case when usage example analysis

First we create the database table:

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;

Insert data:

INSERT INTO `t_demo` VALUES ('1', '张三', '21', '69');
INSERT INTO `t_demo` VALUES ('2', 'Li Si', '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 usage

SELECT
  *,
CASE
  WHEN t.num >= 85 THEN
    'excellent' 
  WHEN t.num < 90 AND t.num>= 60 THEN
    'generally'
  ELSE
    'Failure'
  END AS level
FROM
  t_demo t;

Query structure:

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