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;
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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');
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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;
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