Example
When creating tables it is possible to declare a column as nullable or non-nullable.
CREATE TABLE MyTable
(
MyCol1 INT NOT NULL, -- non-nullable
MyCol2 INT NULL -- nullable
) ;
By default every column (except those in primary key constraint) is nullable unless we explicitly set NOT NULL constraint.
Attempting to assign NULL to a non-nullable column will result in an error.
INSERT INTO MyTable (MyCol1, MyCol2) VALUES (1, NULL) ; -- works fine
INSERT INTO MyTable (MyCol1, MyCol2) VALUES (NULL, 2) ;
-- cannot insert
-- the value NULL into column 'MyCol1', table 'MyTable';
-- column does not allow nulls. INSERT fails.
