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SQL>
SQL> -- Effects of nulls on boolean expressions.
SQL> SET SERVEROUTPUT ON
SQL>
SQL> DECLARE
2 a INTEGER;
3 n INTEGER; -- be our null value.
4 BEGIN
5 -- Assign a value to the variable A, but leave N null.
6 a := 2;
7 -- TIP: try this if you want a null value to be considered "not equal".
8 -- Be careful though, if BOTH A and N are NULL NVL will still return TRUE.
9 IF NVL((a <> n),true) THEN
10 DBMS_OUTPUT.PUT_LINE('The values are not equal.');
11 ELSE
12 DBMS_OUTPUT.PUT_LINE('The values are equal.');
13 END IF;
14 -- TIP: a three-valued IF construct.
15 END;
16 /
The values are not equal.
PL/SQL procedure successfully completed.
SQL>
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