SQL schema for movie rating and seenlist
What does created mean?  When the record was created?  If so, of what use is that?  Perhaps it means when_seen (or rated)?

I see no necessity to separate the two tables.

Since seen is not "optional", and rating is, consider 

rating TINYINT UNSIGNED NULL  COMMENT '1..10'


Where the column is NULL until the user specifies a rating.

NULL has the advantage that

SELECT movie_id, AVG(rating)
    ...


will ignore the NULL values and get the 'correct' average.