Oracle 数据类型分享

给团队内部做的一个Oracle 数据类型分享，主要是关于Oracle数据类型一些内部存储结构及性能介绍。

http://www.slideshare.net/yzsind/oracle-4317768

以下是PPT中unDumpNumber函数的全部代码：

create or replace function unDumpNumber(iDumpStr varchar2) return number is

TYPE ByteArray IS TABLE OF NUMBER INDEX BY BINARY_INTEGER;

Bytes ByteArray;

Result number;

i integer;

pos1 integer;

pos2 integer;

pos3 integer;

vlength integer;

begin

result := 0;

pos1 := instr(iDumpStr, 'Len=') + 4;

pos2 := instr(iDumpStr, ':');

vlength := substr(iDumpStr, pos1, pos2 - pos1);--get length

i := 0;

pos2 := pos2 + 1;

--将dump的字符串填充到数组中

for i in 0..vlength-1

loop

pos3 := instr(iDumpStr, ',', pos2);

if pos3>0 then

Bytes(i) := trim(substr(iDumpStr, pos2, pos3 - pos2 ));

else

Bytes(i) := trim(substr(iDumpStr, pos2));--最后1字节

end if;

pos2 := pos3 + 1;

end loop;

--还原NUMBER

if Bytes(0) = 128 then --128表示0

result := 0;

elsif Bytes(0) > 128 then --大于128表示正数

for i in 1 .. vlength - 1 loop

result := result +

(Bytes(i) - 1) * power(100, (Bytes(0) - 193) - i+1);

end loop;

else --小于128表示负数

for i in 1 .. vlength - 2 loop

result := result +

(Bytes(i) - 101) * power(100, (62 - Bytes(0)) - i+1);

end loop;

end if;

return(Result);

end unDumpNumber;

SQL> select unDumpNumber(dump(314.21)) from dual;

UNDUMPNUMBER(DUMP(314.21))

--------------------------

314.21