text: DROP TABLE if exists thread;
  
  CREATE TABLE thread
  (
      id text not null unique,
      "name" text not null
  );
  
  DROP TABLE if exists email_in_thread;
  
  CREATE TABLE email_in_thread
  (
      email_id text not null,
      thread_id text not null
  );
  
  DROP TABLE if exists member_in_email;
  
  CREATE TABLE member_in_email
  (
      member_email text not null,
      -- role: FROM,TO,CC
      "role" text not null
  );
  
  DROP TABLE if exists intention_email;
  
  CREATE TABLE intention_email
  (
      email_id text not null,
      member_email text not null,
      -- intention: SHARE_OK,SHARE_NG
      "intention" text not null
  );
  