SQL> create table wwm( thechar char(10),thevarchar varchar2(20),thenumber number(10,2));

Table created.

SQL> select * from wwm;

THECHAR    THEVARCHAR            THENUMBER

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

dsffg      varchar2                   10.2

wwm        wwmwwm2                   -999.2

charcharch charcharcharcharchar  100000000

  1* select thechar,dump(thechar) from wwm

SQL> /

THECHAR                                                                                             DUMP(THECHAR)

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

Dsffg                                                                            Typ=96 Len=10: 100,115,102,102,103,32,32,32,32,32

Wwm                                                                           Typ=96 Len=10: 119,119,109,32,32,32,32,32,32,32

Charcharch                                                                    Typ=96 Len=10: 99,104,97,114,99,104,97,114,99,104

可以看到THECHAR是CHAR（ Typ=96）类型的（NCHAR也是96），长度是10（Len=10），不足长度的补空（32）

SQL> select thevarchar,dump(thevarchar) from wwm;

THEVARCHAR                                                                          DUMP(THEVARCHAR)

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

varchar2                                                                                    Typ=1 Len=8: 118,97,114,99,104,97,114,50

wwmwwm2                                                                  Typ=1 Len=7: 119,119,109,119,119,109,50

charcharcharcharchar                                         Typ=1 Len=20: 99,104,97,114,99,104,97,114,99,104,97,114,99,104,97,114,99,104,97,114

可以看到THEVARCHAR是VARCHAR2（ Typ=1）类型的，NVARCHAR2也是1

SQL> select thenumber,dump(thenumber) from wwm;

 THENUMBER                                                                           DUMP(THENUMBER)

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

      10.2                                                                                                Typ=2 Len=3: 193,11,21

    -999.2                                                                                               Typ=2 Len=5: 61,92,2,81,102

 100000000                                                                                           Typ=2 Len=6: 196,100,100,100,100,100

可以看到thenumber是NUMBER（ Typ=2）类型的（FLOAT也是2），

select dump(address,16) from v$sqlarea where rownum = 1;

DUMP(ADDRESS,16)

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

Typ=23 Len=8: 7,0,0,0,47,c9,a4,98

RAW     Typ=23

  1* select thedate,dump(thedate) from wwm6

THEDATE                                                                     DUMP(THEDATE)

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

05-JUN-06                                                                    Typ=12 Len=7: 120,106,6,5,17,16,11

DATE类型Typ=12

CENTURY：120-100=20

Year:       106-100=06

Month=6

Day=5

Hours=17-1=16

Minutes=16-1=16

Seconds=11-1=10

SQL> select sysdate,dump(sysdate) from dual;

SYSDATE                                                                     DUMP(SYSDATE)

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

07-6月 -06                                                                    Typ=13 Len=8: 214,7,6,7,14,57,43,0

SYSDATE是Typ=13

排序，加减等操作就是根据DUMP的结果来排序的（会经过与或等运算，但基数不同，不在这里讨论），

这里只是列出了常用的类型，希望大家以后在读内部结构的时候发现Typ=XX时会想起这篇文章。谢谢