text: alter table topic add column click_count int(11) not null default 0 after reference_count;
  alter table topic add column cover varchar(255) not null after name;
  alter table topic alter column reference_count set default 0;
  
  create table topic_follow
  (
      id        bigint(11) not null,
      user_id   bigint(11) not null,
      topic_id  bigint(11) not null,
      create_at datetime   not null default current_timestamp,
      update_at datetime   not null default current_timestamp,
      primary key (id),
      index idx_topic_id_user_id (topic_id, user_id) using btree
  ) ENGINE = InnoDB
    DEFAULT CHARSET = utf8mb4 COMMENT ='话题关注';