text: --vkontakte_groups_group_members
  
  CREATE UNIQUE INDEX vkontakte_groups_group_members_time_from_3col_uniq
  ON vkontakte_groups_group_members (group_id, user_id, time_from)
  WHERE time_from IS NOT NULL;
  
  CREATE UNIQUE INDEX vkontakte_groups_group_members_time_from_2col_uniq
  ON vkontakte_groups_group_members (group_id, user_id)
  WHERE time_from IS NULL;
  
  CREATE UNIQUE INDEX vkontakte_groups_group_members_time_to_3col_uniq
  ON vkontakte_groups_group_members (group_id, user_id, time_to)
  WHERE time_to IS NOT NULL;
  
  CREATE UNIQUE INDEX vkontakte_groups_group_members_time_to_2col_uniq
  ON vkontakte_groups_group_members (group_id, user_id)
  WHERE time_to IS NULL;
  