Arul,
Thanks for the "Super" nickname, and I am glad that your friend
recommended me. I will answer your questions below:
On 29 May 1999, arul kumar wrote:
>
> Hello Mr.Super(I think it's right name),
>
> This is Arul(rather a ORACLE lover). I came to know about Ur email id thru
> one of my friend. I am very happy to know that Ur responding to the queries
> send to U. I have some quereies too.
>
> 1) What is the actual use of pseudo column Rownum? Can I use it to access a
> specific row in a table?
To access a specific row in a table, use ROWID. The ROWID includes the
datafile, block, and row within the block information. So, if you export
and import the data, the ROWIDs will change.
ROWNUM is used only when selecting data. The FIRST record returned gets
ROWNUM of 1, the SECOND gets ROWNUM of 2, etc. So, the records get ROWNUMs
depending on the order that they are selected. For this reason, you cannot
specify a specific record with ROWNUM. ROWNUM is usually used to limit the
number of records returned:
SELECT * FROM EMP WHERE ROWNUM < 20;
>
> 2) Where actually Savepoints are stored to keep track of the transaction
> done by a user?
They are physically stored in the rollback segments and redo logs. So,
when and if there is a recovery or commit or rollback, Oracle will look in
either the redo logs or the rollback segments. It will roll forward or
rollback depending on the savepoints.
>
> 3) Can I get Recovery steps for Point in time Recovery ?
This is a big questions, because there are many types of recoveries. For
example: missing data datafiles, missing SYSTEM datafiles, missing
rollback segments, missing redo logs, missing controlfiles, etc.
Basically, you recover the database from tape (or select tablespaces
from tape) along with all archived redo logs. Then start up the database
in MOUNT mode and apply redo logs (and sometimes archived redo logs). You
can specify ALL or to recover until a specific redo log or a specific date
and time.
For the full syntax and samples look at the Oracle documentation or
"Oracle Backup and Recovery" by Oracle Press.
>
> 4) How to alter the sequence no. once generated?
Follow the example below:
SQL> create sequence x;
Sequence created.
SQL> select x.nextval from dual;
NEXTVAL
----------
1
1 row selected.
SQL> /
NEXTVAL
----------
2
1 row selected.
SQL> alter sequence x increment by 1000;
Sequence altered.
SQL> select x.nextval from dual;
NEXTVAL
----------
1002
1 row selected.
SQL> /
NEXTVAL
----------
2002
1 row selected.
SQL>
>
> 5) Can U just give me the websites where I can know more about ORACLE.
www.lazydba.com, www.oriolecorp.com, www.orafans.com, www.orafaq.org,
www.ioug.org, www.oracle.com
Don't forget to come back to my page or we'll miss you!
>
> Thanks a lot spending time to see my mail and answering it.(in advance!!)
>
> Regards,
> Arul.
>
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