dual 小研究

上一篇:

http://songhefei.itpub.net/post/7281/216328

SQL> desc dual;

Name Type Nullable Default Comments

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

DUMMY VARCHAR2(1) Y

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

DUMMY DUMP(DUMMY)

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

X Typ=1 Len=1: 88

SQL> select dump('X') from dual;

DUMP('X')

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

Typ=96 Len=1: 88

这里 Type 是不同的，也就是说Oracle 将dual 中的字段的类型是不同于

一般的数据类型的

SQL>select dbms_rowid.rowid_relative_fno(rowid),

dbms_rowid.rowid_block_number(rowid) from dual;

DBMS_ROWID.ROWID_RELATIVE_FNO( DBMS_ROWID.ROWID_BLOCK_NUMBER(

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

1 1618

SQL> alter system dump datafile 1 block 1618;

*** SESSION ID:(12.7) 2008-05-29 17:01:21.000

Start dump data blocks tsn: 0 file#: 1 minblk 1618 maxblk 1618

buffer tsn: 0 rdba: 0x00400652 (1/1618)

scn: 0x0001.6cda07d7 seq: 0x01 flg: 0x06 tail: 0x07d70601

frmt: 0x02 chkval: 0xb694 type: 0x06=trans data

Block header dump: 0x00400652

Object id on Block? Y

seg/obj: 0xde csc: 0x01.6cda07d6 itc: 2 flg: O typ: 1 - DATA

fsl: 0 fnx: 0x0 ver: 0x01

Itl Xid Uba Flag Lck Scn/Fsc

0x01 0x0002.009.000094fb 0x0082180c.0222.15 --U- 1 fsc 0x0000.6cda07d7

0x02 0x0008.01d.0000366a 0x00817b34.01d5.48 C--- 0 scn 0x0000.01063677

data_block_dump,data header at 0x49f105c

===============

tsiz: 0x1fa0

hsiz: 0x14

pbl: 0x049f105c

bdba: 0x00400652

76543210

flag=--------

ntab=1

nrow=1

frre=-1

fsbo=0x14

fseo=0x1f9b

avsp=0x1f83

tosp=0x1f83

0xe:pti[0] nrow=1 offs=0

0x12:pri[0] offs=0x1f9b

block_row_dump:

tab 0, row 0, @0x1f9b

tl: 5 fb: --H-FL-- lb: 0x1 cc: 1

col 0: [ 1] 58

end_of_block_dump

End dump data blocks tsn: 0 file#: 1 minblk 1618 maxblk 1618

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