The below are some of the key points about nulls, and how to compare them. Just to make sure that you should know about what is NULL value.

Interpretation is not exactly missing value.

There could be many reasons why no value is present, e.g., value inappropriate.

How to comapare NULL to values?

In the below example the where condition just checks for TRUE condition. If not matches you will get UNKNOWN.

Example:

Table Name is: Sells

bar          beer    price
================
Joe's bar  Bud   NULL