Good. Finally, we'll refresh your knowledge of
NULL indicates that a value is unknown or missing. You might see a
NULL in a table with clients if you don't have the client's last name (because you forgot to ask!).
You could have a
NULL in the
LaunchDate field of a
Product table if that product hasn't been launched yet.
NULL in a product price field doesn't mean that the product is free; it simply means that we don't know the price.
We use the operators
IS NULL and
IS NOT NULL to check if a value is missing.
IS NULL works like this:
WHERE Category IS NULL;