в 13:45, 26 мая 2010

2010-05-26T13:45:19Z

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2010-05-26T10:00:18Z

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==Assign value not null a null value==



<source lang="sql">

SQL>
SQL> declare
2 myNumber number not null := 1;
3 another_number number;
4 begin
5 myNumber := 2;
6 myNumber := another_number;
7 end;
8 /
declare
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error
ORA-06512: at line 6

SQL>
</source>

==Is Null for a boolean expression==



<source lang="sql">

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 -- NOT NULL = NULL
8 IF (NOT (a = n)) IS NULL THEN
9 DBMS_OUTPUT.PUT_LINE("NOT NULL = NULL");
10 END IF;
11 END;
12 /
NOT NULL = NULL
PL/SQL procedure successfully completed.
SQL>

</source>

==NVL deals with a boolean expression==



<source lang="sql">
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>

</source>

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Oracle PL/SQL/PL SQL/Null Value - История изменений

в 13:45, 26 мая 2010

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