| 21. 24. 1. All logical operations (including NOT) involving NULL always return NULL |
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In a logical group of IF/THEN/ELSE or CASE statements, NULL is interpreted as FALSE. |
Most operations (built-in functions, arithmetic) with any NULL operand return NULL with the following exceptions: |
Concatenations of strings ignore NULL. |
DECODE (which we discuss later) can compare values with NULL. |
The REPLACE function can take NULL as a third parameter. |
You should check for NULL values by using the syntax: |
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variable|expression|function IS [NOT] NULL
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This structure evaluates the value against NULL. |
You can check equality by using IS NULL or inequality by using IS NOT NULL. |
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SQL>
SQL> declare
2 v1 NUMBER;
3 v2 NUMBER :=1;
4 begin
5 if v1 is null then
6 DBMS_OUTPUT.put_line('v1 is NULL');
7 elsif v1 is not null then
8 DBMS_OUTPUT.put_line('v1 is not NULL');
9 else
10 DBMS_OUTPUT.put_line('Undefined result');
11 end if;
12
13 if v2 is null then
14 DBMS_OUTPUT.put_line('v2 is NULL');
15 elsif v2 is not null then
16 DBMS_OUTPUT.put_line('v2 is not NULL');
17 else
18 DBMS_OUTPUT.put_line('Undefined result');
19 end if;
20 end;
21 /
v1 is NULL
v2 is not NULL
PL/SQL procedure successfully completed.
SQL>
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