text: 
  CREATE VIEW conversation_info (id, last_author_date, last_change_date) AS
  SELECT c.id, GREATEST(MAX(cm.author_date), c.create_date), GREATEST(MAX(cm.last_change), c.create_date)
  FROM conversation c
  LEFT JOIN conversation_message cm ON cm.conversation_id = c.id
  GROUP BY c.id;
  
  
  CREATE VIEW member_info (id, last_author_date, last_change_date) AS
  SELECT m.id, GREATEST(MAX(cm.author_date), m.join_date), GREATEST(MAX(cm.last_change), m.join_date)
  FROM member m
  LEFT JOIN conversation_message cm ON cm.conversation_id = m.conversation_id
  GROUP BY m.id;