| Column data in Oracle block [message #173387] |
Mon, 22 May 2006 04:37  |
gajini
Messages: 262
Registered: January 2006
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Senior Member |
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Consider a table having 3 columns,namely EMP(c1,c2,c3)
Using data block header,Oracle identifies that a block containing rows
for EMP table.My doubt in this is,
In the row data of a block,how oracle identifies that this piece of data belong to a particular column(i.e.,column data) of EMP table i.e,how it identifies this portion of data belongs to C1,C2 & C3? Is oracle following any offset mechanism for this classification?Please suggest your answers
& views on this question.
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| Re: Column data in Oracle block [message #173400 is a reply to message #173387] |
Mon, 22 May 2006 05:31  |
Frank Naude
Messages: 4580
Registered: April 1998
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Senior Member |
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Column offsets are stored in the data dictionary (SYS.COL$). The positions of fixed length types can easily be determined. Variable length types like VARCHAR2 are length prefixed.
SQL> SELECT col#, name, type#, length
2 FROM col$
3 WHERE obj# = (SELECT obj#
4 FROM obj$
5 WHERE name = 'EMP'
6 AND owner# = (SELECT user#
7 FROM user$
8 where name = 'SCOTT'))
9 /
COL# NAME TYPE# LENGTH
---------- ------------------------------ ---------- ----------
1 EMPNO 2 22
2 ENAME 1 10
3 JOB 1 9
4 MGR 2 22
5 HIREDATE 12 7
6 SAL 2 22
7 COMM 2 22
8 DEPTNO 2 22
8 rows selected. |
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