What is null
Before we discuss null first let’s look at the students information.
In the students table scroll down and see the age of “Edgar” or of “Tonya”. We do not have age information for them.
Similarly, look at the grade information for “Abraham” or course information for “Hugh”. These information are also missing.
So how do we capture the information that this data is missing. We can’t put zero here because their age or grade is not zero.
A grade of zero means that the student got zero grade. However it is different from grade information is missing.
In database we represent missing information as NULL.