What is the role of NOTNULL in the statement 'AAA' varchar (11) NOTNULL when creating a field? -Php Tutorial

What is the role of NOTNULL in the statement 'AAA' varchar (11) NOTNULL when creating a field? When creating a field, what is the function of the statement 'AAA' varchar (11) not null?
Not null?

Reply to discussion (solution)

This field cannot be blank (null). That is, when a record is inserted, this field must have a value.
Not null? Yes, of course, but it depends on your business.

Not null indicates that this field cannot be null when you insert it.
Remember, null is different from null. the null string is :''

The database can declare not null default''

In this case, data is inserted. if this field is not declared, it is stored as a null string by default.

There are many reasons for not null. one of the reasons is that a field in the database is null, which indicates null, the string is null after you obtain it.

When inserting data, the field cannot be blank and must have a value.