字符类型：
SQL> select dump('Whoami') from dual;
DUMP('WHOAMI')
-----------------------------------
Typ=96 Len=6: 87,104,111,97,109,105这个是变长。
SQL> select name,dump(name) from cha;
NAME DUMP(NAME)
--------------------------------------------------------------------------------
fun Typ=96 Len=10: 102,117,110,32,32,32,32,32,32,32后面这些32就是用来填充的。
SQL> select dump(-98765.432) from dual; 1-127负数，128以上正数。指数计算：见下方。
DUMP(-98765.432)
----------------------------------
Typ=2 Len=7: 60,92,14,36,58,81,102 62- first byte =2（指数）->first byte =60; 101 -9=92,101-87=14...
SQL> select dump(98765.432) from dual;
DUMP(98765.432)
-------------------------------
Typ=2 Len=6: 195,10,88,66,44,21 first byte-193=2 ->first byte =195; x-1=10,x-1=87...
