Recipe 2. Retrieving a Subset of Rows from a Table

Problem
You have a table and want to see only rows that satisfy a specific condition.

Solution
Use the WHERE clause to specify which rows to keep. For example, to view all employees assigned to department number 10:

1 select *
2   from emp
3  where deptno = 10

Discussion
The WHERE clause allows you to retrieve only rows you are interested in. If the expression in the WHERE clause is true for any row, then that row is returned.

Most vendors support common operators such as: =, <, >, <=, >=, !, <>. Additionally, you may want rows that satisfy multiple conditions; this can be done by specifying AND, OR, and parenthesis .

Recipe 1.Retrieving All Rows and Columns from a Table

Problem
You have a table and want to see all of the data in it.

Solution
Use the special “*” character and issue a SELECT against the table:

1 select *
2 from emp

Discussion
The character “*” has special meaning in SQL. Using it will return every column for the table specified. Since there is no WHERE clause specified, every row will be returned as well. The alternative would be to list each column individually:

select empno,ename,job,sal,mgr,hiredate,comm,deptno
from emp
In ad hoc queries that you execute interactively, it’s easier to use SELECT *. However, when writing program code it’s better to specify each column individually. The performance will be the same, but by being explicit you will always know what columns you are returning from the query. Likewise, such queries are easier to understand by people other than yourself (who may or may not know all the columns in the tables in the query).

Reset Windows Password /w KNOPPIX.

If you forget a password for your user on your Windows system (especially if the user is administrator), your computer immediately becomes a paperweight. It’s like being locked out of your car without a spare set of keys and without a way to contact a locksmith. Use Knoppix as your locksmith to reset the password to a new value or even completely erase it.

User accounts have an interesting history in Windows. The Windows 9x series did offer usernames and passwords, but every user could overwrite every other user’s files, and the system did not offer any real security. If you forget your password in Windows 9x, resetting it is as simple as deleting a .pwd file with a DOS disk. With Windows NT, 2000, and XP, Microsoft has increased its user security by creating different user accounts on the same system and passwords that protect them. However, unlike in Windows 9x, if you forget your Administrator password, your only recourse is to purchase a tool to reset your Windows password or to reinstall Windows to create a new administrator account. If you have a Knoppix disc, you can download and use the chntpw tool, which is a small program that lets you reset the local passwords on a Windows system, and return to your system.

Get chntpw

The chntpw tool is part of the ntpasswd package, which can be downloaded in boot floppy form from its web site at http://home.eunet.no/~pnordahl/ntpasswd/. However, this gives you a floppy image and requires that you mount multiple loopback entries to extract the utility from the floppy image to use under Knoppix. While you can simply create an ntpasswd boot floppy, this means yet another rescue disk to carry with you, and the beauty of Knoppix is that you have access to all of your recovery tools in a single disc. Luckily, the chntpw tool is now part of Debian unstable, which means that you can grab it directly from Debian’s repository.

You could use the apt-get wrapper, which is included for Knoppix, to download chntpw. However, to be certain you retrieve the latest version of chntpw, you must run the apt-get update, which downloads about 10 times as much data per repository as the 85-KB chntpw package. It saves bandwidth and time to download the package directly.

Fix The Windows Boot.ini file with KNOPPIX!![2]

One thing that has been missing from Knoppix (and Linux in general) is the ability to safely write to NTFS partitions. Now with Knoppix 3.4, you can edit, delete, and move files on your NTFS partition—jobs that are difficult with the Windows Recovery CD!

While the Linux kernel has been able to read NTFS partitions for some time, writing to them has always been considered very dangerous. The NTFS spec is a closed spec that requires kernel hackers to reverse engineer it to make a driver that supports it. However, this can be very problematic: if a programmer reverse engineers NTFS 3.0, she must repeat the process when NTFS 4.0 is released. Writing to NTFS has been so dangerous that instead of just warning users, some kernels go as far as disabling write support in the NTFS driver itself. Recently, a solution to write to NTFS partitions has appeared with Captive NTFS. This solution actually uses the NTFS drivers that Windows itself uses, and is included in Knoppix 3.4.

Captive NTFS is still somewhat experimental, and while it has worked for many people, there is a chance for data loss, so be sure to back up any important files on filesystems you mount this way.

Configure Captive NTFS

The Knoppix Captive NTFS wizard makes it easy to configure and use the Captive NTFS system. When you run the wizard, it scans all the drives on your computer for the Microsoft-provided NTFS drivers it needs to safely write to your NTFS filesystems. Click K Menu|KNOPPIXUtilities|Captive NTFS to launch the program. The wizard that appears automates the process of finding and using the NTFS .dlls. Click Forward to see a listing of the system files that Captive NTFS has already found on your Knoppix system. Click Forward again, and the wizard mounts and scans your hard drives for the essential files it needs.

Fix The Windows Boot.ini file with KNOPPIX!!

If a Windows boot.ini file gets corrupted, you might find yourself unable to boot back into Windows. While the Windows Recovery CD can restore a default boot file, unlike Knoppix, it won’t let you edit it directly.

Back in the old days of Windows, you could change many different startup settings by editing .ini files that were in the root of your hard drive. Over the years, Microsoft has moved most of the settings that control configuration to the registry, but there is one important file that remains, boot.ini. In this file, you can find information that the Windows boot loader uses to determine booting options and, in the case of more than one Windows OS on a system, which OS to boot. For example, this is a boot.ini file that allows you to boot between Windows 2000 and Windows XP Professional:

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)WINNT
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)WINNT="Windows 2000" /fastdetect
multi(0)disk(0)rdisk(0)partition(2)WINDOWS="Windows XP Professional"
/fastdetect

This file is split into two parts: the part that contains settings for the boot loader that starts with [boot loader] and the part that containing the different operating systems available for booting that starts with [operating systems]. The first option, timeout, controls how many seconds the boot loader waits before booting the default operating system. The default option tells the boot loader which operating system to boot if the timeout has passed.