MySQL NOT IN from another column in the same table

Question

I want to run a mysql query to select all rows from a table films where the value of the title column does not exist anywhere in all the values of another column (collection).

Here is a simplified version of my table with content:

mysql> select * from films;
+----+--------------+--------------+
| id | title        | collection   |
+----+--------------+--------------+
|  1 | Collection 1 | NULL         |
|  2 | Film 1       | NULL         |
|  3 | Film 2       | Collection 1 |
+----+--------------+--------------+

Here is my query:

mysql> SELECT * FROM films WHERE title NOT IN (SELECT collection FROM films);
Empty set (0.00 sec)

In this example, I would want to select the rows with titles Film 1 and Film 2, but my query is returning no rows.

Here is the table structure:

CREATE TABLE `films` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `title` varchar(200) NOT NULL DEFAULT '',
  `collection` varchar(200) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM;

Answer 1

SELECT * 
FROM films 
WHERE title NOT IN (SELECT collection FROM films where collection is not null);

SQLFiddle: http://sqlfiddle.com/#!2/76278/1

Answer 2

Have you tried using NOT EXISTS:

SELECT * 
FROM films f1
WHERE NOT EXISTS (SELECT collection 
                  FROM films f2
                  WHERE f1.title = f2.collection);

See SQL Fiddle with Demo

If you want to use IN then you will want to look for values that are NOT NULL:

SELECT * 
FROM films 
WHERE title NOT IN (SELECT collection 
                    FROM films
                    WHERE collection is not null);

See SQL Fiddle with Demo

The result for both is:

| ID |  TITLE |   COLLECTION |
------------------------------
|  2 | Film 1 |       (null) |
|  3 | Film 2 | Collection 1 |

The problem with your current query is that -- stealing from @Quassnoi's answer here:

Both IN and NOT IN return NULL which is not an acceptable condition for WHERE clause.

Since the null value is being returned by your subquery you want to specifically exclude it.