创建 create
CREATE INDEX ... ON table_name (column)
  [UNIQUE INDEX -- 唯一索引
  |FULLTEXT INDEX -- 全文索引
  ] INDEX index_name -- 不指定唯一或全文时默认普通索引
  注意要用分号做好每段创建的连接

create index idx_duration on examination_info(duration);
create unique index uniq_idx_exam_id on examination_info(exam_id);
create fulltext index full_idx_tag on examination_info(tag)