text: create table tags (
    `id` bigint(20) NOT NULL auto_increment,
    `name` varchar(255) NOT NULL,
    primary key (`id`),
    UNIQUE KEY `I_name` (`name`)
  ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
  
  create table taggings (
    `id` bigint(20) NOT NULL auto_increment,
    `post_id` bigint(20) NOT NULL,
    `tag_id` bigint(20) NOT NULL,
    PRIMARY KEY (`id`),
    UNIQUE KEY `I_post_id` (`post_id`,`tag_id`),
    KEY `I_tag_id` (`tag_id`,`post_id`)
  ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;
  
  alter table posts drop column tags, drop column source, drop column source_uri;
  drop table post_commands;