[20180927]ora-01426.txt

--//链接:http://www.itpub.net/thread-2105458-1-1.html
1.环境:
SCOTT@test01p> @ ver1

PORT_STRING VERSION BANNER CON_ID
------------------------------ -------------- -------------------------------------------------------------------------------- ----------
IBMPC/WIN_NT64-9.1.0 12.1.0.1.0 Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production 0

set serveroutput on

DECLARE
L_NUMBER number;
BEGIN
L_NUMBER := 1024 * 1024 * 1024 * 1024;
DBMS_OUTPUT.PUT_LINE(L_NUMBER);
END;
/

DECLARE
*
ERROR at line 1:
ORA-01426: numeric overflow
ORA-06512: at line 4

--//1024*1024 = 1048576
--//1048576*1048576 = 1099511627776

d:\blog>oerr ora 1426
01426, 00000, "numeric overflow"
// *Cause: Evaluation of an value expression causes an overflow/underflow.
// *Action: Reduce the operands.

DECLARE
L_NUMBER number;
BEGIN
L_NUMBER := 1024 * 1024 * 1024 * 1024.0;
DBMS_OUTPUT.PUT_LINE(L_NUMBER);
END;
/

1099511627776
PL/SQL procedure successfully completed.
--//使用小数点,等于浮点运算,出现类型转换.
--//写成如下,一样通过,也证明没有溢出:

DECLARE
L_NUMBER number;
BEGIN
L_NUMBER := 1024 * 1024 * 1024;
L_NUMBER :=L_NUMBER *1024 *1024*1024;
DBMS_OUTPUT.PUT_LINE(L_NUMBER);
END;
/

1152921504606846976
PL/SQL procedure successfully completed.

SCOTT@test01p> set serverout on
SCOTT@test01p> DECLARE
2    L_NUMBER number;
3 BEGIN
4      L_NUMBER := 2147483647-1+1;
5      L_NUMBER := 2147483647+1-1;
6       DBMS_OUTPUT.PUT_LINE(L_NUMBER);
7 END;
8 /
DECLARE
*
ERROR at line 1:
ORA-01426: numeric overflow
ORA-06512: at line 5

--//很明显oracle在一个算式里面达到2^31 就报错.改成如下也不会报错

DECLARE
L_NUMBER number;
BEGIN
   -- L_NUMBER := 2147483647-1+1;
    L_NUMBER := 2147483647;
    L_NUMBER := L_NUMBER+1-1;
     DBMS_OUTPUT.PUT_LINE(L_NUMBER);
END;
/

2147483647
PL/SQL procedure successfully completed.