Comparision with NULL

Good job. Remember, NULL is a special value. It means that some piece of information is missing or unknown.

If you set a condition on a particular column, say AGE < 70, the rows where age is NULL will always be excluded from the results. Let's check that in practice.

In no way does NULL equal zero. What's more, the expression NULL = NULL is never true in SQL!
Exercise

Select all columns for cars whose price column is greater than or equal to zero.

Note that the Opel with an unknown price is not in the result.