SQL DISTINCT when combining LEFT JOIN with subquery

I have the following two SQL tables for storing movie titles, and the dates I've seen them:

CREATE TABLE movies (
  id int(10) unsigned NOT NULL AUTO_INCREMENT,
  title varchar(90) NOT NULL,
  year varchar(7) DEFAULT NULL,
  watchAgain enum('0', '1') NOT NULL DEFAULT '0',
  PRIMARY KEY (id)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=3 ;

INSERT INTO movies (id, title, year, watchAgain) 
  VALUES (1, 'Wall Street', '1987', '1'), (2, 'Wag the Dog', '1997', '1');

CREATE TABLE movies_seen (
  object_id int(10) NOT NULL DEFAULT '0',
  date varchar(10) CHARACTER SET utf8 COLLATE utf8_unicode_ci 
    NOT NULL DEFAULT '0',
  seen_again enum('0', '1') NOT NULL DEFAULT '0',
  PRIMARY KEY (object_id, date)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

INSERT INTO `movies_seen` (object_id, date, seen_again)   
  VALUES (1, '1156187700', '0'), (1, '1218395700', '0'), (2, '0', '0');

To find movies I should watch again, I ask the database for titles with seen_again == 1, or if seen_again == 0 and it is not stored in movies_seen:

SELECT m.year, m.title, s.date AS last_seen
FROM movies m 
LEFT JOIN movies_seen s ON m.id = s.object_id
WHERE 
     (
     m.watchAgain = '0'
     AND m.id NOT IN (SELECT s.开发者_如何学Cobject_id 
                      FROM movies m 
                      INNER JOIN movies_seen s ON m.id = s.object_id)
    OR m.watchAgain = '1'
    )
ORDER BY m.title

This basically works, but when the movies_seen table has 2 entires for the same title, it shows up duplicated in the results:

year    title           last_seen 
1997    Wag the Dog 0
1987    Wall Street 1156187700
1987    Wall Street 1218395700

It works with DISTINCT if I only fetch the title, but as I need additional columns, this obviously fails. Ideas?

In MySQL a GROUP BY clause can do the same task as a DISTINCT

SELECT m.year
  , m.title
  , s.date AS last_seen 
FROM movies m  
LEFT JOIN movies_seen s ON m.id = s.object_id 
WHERE (m.watchAgain = '0'             
  AND m.id NOT IN (SELECT s.object_id 
                   FROM movies m 
                   INNER JOIN movies_seen s ON m.id = s.object_id)             
  OR m.watchAgain = '1') 
GROUP BY m.title /*<<--- this will do a distinct on title only*/
ORDER BY m.title 

AFAIK, this only works on MySQL.

BTW: Since you are grouping on m.title MySQL does a sort on title, so the ORDER BY clause is not technically needed anymore.

SELECT m.year, m.title, s.date AS last_seen
FROM movies m 
WHERE exists  
    ( 
      select 1 from movies_seen s 
          where m.id = s.object_id 
           and ( m.watchAgain = '0'
            AND m.id NOT IN (SELECT s.object_id FROM movies m INNER JOIN movies_seen s ON m.id = s.object_id)
            OR m.watchAgain = '1'
            )
    )
ORDER BY m.title