Question

I wanna create a table in SQL, and if the I wanna set the attributes to NULL, how do I do it?
For example, I wanna create a table named Courses and its attributes “CourseNo” and “Title” must not be null. I created one below:

CREATE TABLE Courses(
    CourseNo INTEGER CHECK(100<=CourseNo<=999) PRIMARY KEY,
    Title VARCHAR(100),
    )

ALTER TABLE Courses
ALTER COLUMN CourseNo INTEGER NOT NULL
ALTER COLUMN Title VARCHAR(100) NOT NULL

Is this correct?

Answer 1

whatever you wrote that one correct but good practice is to write not null at a time of defining table.
do like this:

CREATE TABLE Courses(
    CourseNo INTEGER CHECK(100<=CourseNo<=999) PRIMARY KEY,
    Title VARCHAR(100) NOT NULL,
    )

primary key is by default NOT NULL always, hence you no need to declare it as NOT NULL

NOT NULL in alter is used when u want to make change in column definations of table later