NOT NULL Constraint
By default, a column can hold NULL values.
The NOT NULL Constraint used to makes sure that a column does not hold NULL value.
SQL NOT NULL - CREATE TABLE
The following SQL Query ensures that the "ID", "FULL_NAME", and "COUNTRY" columns will NOT accept NULL values when the "STUDENTS" table is created:
CREATE TABLE STUDENTS (
ID INT NOT NULL,
FULL_NAME VARCHAR (200) NOT NULL,
ADDRESS VARCHAR (200),
CITY VARCHAR (200),
COUNTRY VARCHAR (200) NOT NULL
PRIMARY KEY (ID)
);
SQL NOT NULL - ALTER TABLE
ALTER TABLE STUDENTS
MODIFY ADDRESS VARCHAR (200) NOT NULL;