SELECT *\nFROM\n table1 one\n LEFT OUTER JOIN table2 two ON(two.key = one.key)\nWHERE\n (one.Column1 != two.Column2) OR\n ((one.Column IS NULL) AND (two.Column IS NOT NULL)) OR\n ((one.Column IS NOT NULL) AND (two.Column IS NULL))
Or you can just stack up a bunch of tests in the WHERE clause.