By this point of the lesson, you might have noticed that there are a few missing values in the movies table. More often than not, the data you encounter will have missing values.

Unknown values are indicated by NULL.

It is not possible to test for NULL values with comparison operators, such as = and !=.

Instead, we will have to use these operators:

• IS NULL
• IS NOT NULL

To filter for all movies with an IMDb rating:

SELECT name
FROM movies 
WHERE imdb_rating IS NOT NULL;