Oracle 中关于超过253列内部数据的存储

建表语句declare v_sql varchar2(32767) ;begin v_sql :=

建表语句
declare
v_sql varchar2(32767) ;
begin
v_sql := 'create table test ( ' ;
for i in 1..500 loop
v_sql := v_sql || 'name'||i||' varchar2(2000) ,' ;
end loop ;
v_sql := substr(v_sql,1,length(v_sql)-1) ;
v_sql := v_sql || ');' ;
dbms_output.put_line(v_sql) ;
end ;
复制粘贴创建表

_dex@DAVID> desc test
Name Null? Type
----------------------------------------------------- -------- ------------------------------------
NAME1 VARCHAR2(2000)
NAME2 VARCHAR2(2000)
NAME3 VARCHAR2(2000)
.....
NAME500 VARCHAR2(2000)

_dex@DAVID> insert into test (name500) values (lpad(1,300,'d')) ;

1 row created.


_dex@DAVID> select
2 length(t.name500),
3 dbms_rowid.rowid_relative_fno(t.rowid) as "FNO#",
4 dbms_rowid.rowid_block_number(t.rowid) as "BLK#",
5 dbms_rowid.rowid_row_number(t.rowid) as "ROW#"
6 from dex.test t
7 /

LENGTH(T.NAME500) FNO# BLK# ROW#
----------------- ---------- ---------- ----------
300 4 925 1
1 4 925 3
300 4 925 5


使用bbed查看

首先看row#为1长度为300的数据
BBED> set dba 4,925
DBA 0x0100039d (16778141 4,925)

BBED> p kdbr
sb2 kdbr[0] @142 7504
sb2 kdbr[1] @144 7250
sb2 kdbr[2] @146 6991
sb2 kdbr[3] @148 6737
sb2 kdbr[4] @150 6177
sb2 kdbr[5] @152 5923

BBED> p *kdbr[1]
rowdata[1327]
-------------
ub1 rowdata[1327] @7374 0x28

BBED> dump /v offset 7374 count 128
File: /u01/apps/Oracle/oradata/david/users01.dbf (4)
Block: 925 Offsets: 7374 to 7501 Dba:0x0100039d
-------------------------------------------------------
2801f501 00039d00 00ffffff ffffffff l (.õ.............
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................
ffffffff ffffffff ffffffff ffffffff l ................

<16 bytes per line>

这些是row piece header
2801f501 00039d00 00

1个字节的flag=28
16进制28=二进制00101000=--H-F---=head of rowpiece + first data piece
1个字节的lb(itl slot)=01
1个字节的cc column count=f5=245 (因为最后一列name500不为空,所以null都需要使用ff来表示,也就是说需要存储500列的数据)