You can add the NOT NULL constraint on a scalar variable or constant.
You can also add NOT NULL constraint on scalar component of a composite variable.
The NOT NULL constraint prevents assigning a null value to the variable.
The variable can have this constraint either implicitly from its data type or explicitly.
A NOT NULL scalar variable declaration must assign an initial value to the variable because the default initial value for a scalar variable is NULL.
In the following code, the variable my_id has the NOT NULL constraint explicitly, and the variables a, b, and c acquire it from their data types.
SQL> SQL> DECLARE-- w ww .ja va 2s. c o m 2 my_id INTEGER(4) NOT NULL := 9999; 3 a NATURALN := 9999; 4 b POSITIVEN := 9999; 5 c SIMPLE_INTEGER := 9999; 6 BEGIN 7 DBMS_OUTPUT.PUT_LINE(my_id); 8 DBMS_OUTPUT.PUT_LINE(a); 9 DBMS_OUTPUT.PUT_LINE(b); 10 DBMS_OUTPUT.PUT_LINE(c); 11 NULL; 12 END; 13 / 9999 9999 9999 9999 PL/SQL procedure successfully completed. SQL>