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CREATE TABLE `students` (
  `id` bigint(32) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `name` varchar(64) NOT NULL COMMENT '姓名',
  `age` int(11) NOT NULL COMMENT '年纪',
  `class` int(11) NOT NULL COMMENT '班级',
  `created_at` datetime NOT NULL COMMENT '创建时间',
  `updated_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  PRIMARY KEY (`id`),
  KEY `idx_class` (`class`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=608 DEFAULT CHARSET=utf8mb4 COMMENT='学生表';

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select table_schema,table_name,index_name,cardinality from information_schema.statistics where table_schema='database' and table_name = 'students' order by cardinality desc