By default all columns accept NULL values. SQL NOT NULL Constraint indicates that the column will not accept NULL values. NOT NULL Constraint can only be used as a column Constraint. It is not supported for table or domain constraints.
Example of SQL NOT NULL Constraint
The price of the beer cannot be NULL in the below Create Table query:
CREATE TABLE Sells ( bar CHAR(20), beer VARCHAR(20) DEFAULT 'Kingfisher', price REAL NOT NULL, PRIMARY KEY (bar,beer) );