Monday, December 31, 2012
Saturday, December 29, 2012
General Questions on SQL SERVER
What is RDBMS?
Relational Data Base Management Systems (RDBMS) are database management systems that maintain data records and indices in tables. Relationships may be created and maintained across and among the data and tables. In a relational database, relationships between data items are expressed by means of tables. Interdependencies among these tables are expressed by data values rather than by pointers. This allows a high degree of data independence. An RDBMS has the capability to recombine the data items from different files, providing powerful tools for data usage. (Read more here)
What are the Properties of the Relational Tables?
Relational tables have the following six properties:
- Values are atomic.
- Column values are of the same kind.
- Each row is unique.
- The sequence of columns is insignificant.
- The sequence of rows is insignificant.
- Each column must have a unique name.
What is Normalization?
Database normalization is a data design and organization process applied to data structures based on rules that help building relational databases. In relational database design, the process of organizing data to minimize redundancy is called normalization. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables. The objective is to isolate data so that additions, deletions, and modifications of a field can be made in just one table and then propagated through the rest of the database via the defined relationships.
What is De-normalization?
De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. It is sometimes necessary because current DBMSs implement the relational model poorly. A true relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access.
How is ACID property related to Database?
ACID (an acronym for Atomicity Consistency Isolation Durability) is a concept that Database Professionals generally look for while evaluating databases and application architectures. For a reliable database, all this four attributes should be achieved.
Atomicity is an all-or-none proposition.
Consistency guarantees that a transaction never leaves your database in a half-finished state.
Isolation keeps transactions separated from each other until they are finished.
Durability guarantees that the database will keep track of pending changes in such a way that the server can recover from an abnormal termination. (Read more here)
What are the Different Normalization Forms?
1NF: Eliminate Repeating Groups
Make a separate table for each set of related attributes, and give each table a primary key. Each field contains at most one value from its attribute domain.
2NF: Eliminate Redundant Data
If an attribute depends on only part of a multi-valued key, then remove it to a separate table.
3NF: Eliminate Columns Not Dependent On Key
If attributes do not contribute to a description of the key, then remove them to a separate table. All attributes must be directly dependent on the primary key. (Read more here)
BCNF: Boyce-Codd Normal Form
If there are non-trivial dependencies between candidate key attributes, then separate them out into distinct tables.
4NF: Isolate Independent Multiple Relationships
No table may contain two or more 1:n or n:m relationships that are not directly related.
5NF: Isolate Semantically Related Multiple Relationships
There may be practical constrains on information that justify separating logically related many-to-many relationships.
ONF: Optimal Normal Form
A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.
DKNF: Domain-Key Normal Form
A model free from all modification anomalies is said to be in DKNF.
Remember, these normalization guidelines are cumulative. For a database to be in 3NF, it must first fulfill all the criteria of a 2NF and 1NF database.
ACID PROPERTIES
ACID (an acronymn for Atomicity Consistency Isolation Durability) is a concept that Database Professionals generally look for when evaluating databases and application architectures. For a reliable database all this four attributes should be achieved.
Atomicity is an all-or-none proposition.
Consistency guarantees that a transaction never leaves your database in a half-finished state.
Isolation keeps transactions separated from each other until they’re finished.
Durability guarantees that the database will keep track of pending changes in such a way that the server can recover from an abnormal termination.
SQL SERVER IV
http://blog.sqlauthority.com/sql-server-interview-questions-and-answers/
Friday, December 28, 2012
SQL Server Tutorial
Server Database Systems
Server based database systems are designed to run on a central server, so that multiple users can access the same data simultaneously. The users normally access the database through an application.
For example, a website could store all its content in a database. Whenever a visitor views an article, they are retrieving data from the database. As you know, websites aren't normally limited to just one user. So, at any given moment, a website could be serving up hundreds, or even thousands of articles to its website visitors. At the same time, other users could be updating their personal profile in the members' area, or subscribing to a newsletter, or anything else that website users do.
Generally, it's the application that provides the functionality to these visitors. It is the database that stores the data and makes it available. Having said that, SQL Server does include some useful features that can assist the application in providing its functionality.
Here are the different editions available for SQL Server 2008.
Here are the different editions available for SQL Server 2008.
- Enterprise Edition
Data management and business intelligence platform providing enterprise class scalability, high availability, and security for running business-critical applications - Standard Edition
Data management and business intelligence platform providing ease of use and manageability for running departmental applications - Workgroup Edition
Data management and reporting platform providing secure, remote synchronization, and management capabilities for running branch applications - Developer Edition
May be installed and used by one user to design, develop, test, and demonstrate your programs on as many systems as needed - Web Edition
A low-TCO, scalable, and manageable database option for web hosters and end customers looking to deploy publicly facing web applications and services - Express Edition
A free edition of SQL Server ideal for learning and building desktop and small server applications and for redistribution by ISVs - Compact Edition
A free, SQL Server embedded database ideal for building stand-alone and occasionally connected applications for mobile devices, desktops, and web clients - Evaluation Edition
This edition may be installed for demonstration and evaluation purposes until an expiration period of 180 days.
Wednesday, December 26, 2012
Linux Shell Commands Cheat Sheet
Examples marked with * are valid and safe to paste into a linux terminal without modification.
Command | Description | |
* | apropos whatis | Show commands pertinent to string. See also threadsafe |
* | man -t man | ps2pdf – > man.pdf | make a pdf of a manual page |
which command | Show full path name of command | |
time command | See how long a command takes | |
* | time cat | Start stopwatch. Ctrl-d to stop. See also sw |
* | nice info | Run a low priority command (The “info” reader in this case) |
* | renice 19 -p $$ | Make shell (script) low priority. Use for non interactive tasks |
* | cd - | Go to previous directory |
* | cd | Go to $HOME directory |
(cd dir && command) | Go to dir, execute command and return to current dir | |
* | pushd . | Put current dir on stack so you canpopd back to it |
* | alias l=’ls -l –color=auto’ | quick dir listing |
* | ls -lrt | List files by date. See also newest andfind_mm_yyyy |
* | ls /usr/bin | pr -T9 -W$COLUMNS | Print in 9 columns to width of terminal |
find -name ‘*.[ch]‘ | xargs grep -E ‘expr’ | Search ‘expr’ in this dir and below. See also findrepo | |
find -type f -print0 | xargs -r0 grep -F ‘example’ | Search all regular files for ‘example’ in this dir and below | |
find -maxdepth 1 -type f | xargs grep -F ‘example’ | Search all regular files for ‘example’ in this dir | |
find -maxdepth 1 -type d | while readdir; do echo $dir; echo cmd2; done | Process each item with multiple commands (in while loop) | |
* | find -type f ! -perm -444 | Find files not readable by all (useful for web site) |
* | find -type d ! -perm -111 | Find dirs not accessible by all (useful for web site) |
* | locate -r ‘file[^/]*\.txt’ | Search cached index for names. This re is like glob *file*.txt |
* | look reference | Quickly search (sorted) dictionary for prefix |
* | grep –color reference /usr/share/dict/words | Highlight occurances of regular expression in dictionary |
gpg -c file | Encrypt file | |
gpg file.gpg | Decrypt file | |
tar -c dir/ | bzip2 > dir.tar.bz2 | Make compressed archive of dir/ | |
bzip2 -dc dir.tar.bz2 | tar -x | Extract archive (use gzip instead of bzip2 for tar.gz files) | |
tar -c dir/ | gzip | gpg -c | ssh user@remote ‘dd of=dir.tar.gz.gpg’ | Make encrypted archive of dir/ on remote machine | |
find dir/ -name ‘*.txt’ | tar -c –files-from=- | bzip2 > dir_txt.tar.bz2 | Make archive of subset of dir/ and below | |
find dir/ -name ‘*.txt’ | xargs cp -a –target-directory=dir_txt/ –parents | Make copy of subset of dir/ and below | |
( tar -c /dir/to/copy ) | ( cd /where/to/ && tar -x -p ) | Copy (with permissions) copy/ dir to /where/to/ dir | |
( cd /dir/to/copy && tar -c . ) | ( cd /where/to/ && tar -x -p ) | Copy (with permissions) contents of copy/ dir to /where/to/ | |
( tar -c /dir/to/copy ) | ssh -C user@remote ‘cd /where/to/ && tar -x -p’ | Copy (with permissions) copy/ dir to remote:/where/to/ dir | |
dd bs=1M if=/dev/sda | gzip | ssh user@remote ‘dd of=sda.gz’ | Backup harddisk to remote machine | |
rsync -P rsync://rsync.server.com/path/to/file file | Only get diffs. Do multiple times for troublesome downloads | |
rsync –bwlimit=1000 fromfile tofile | Locally copy with rate limit. It’s like nice for I/O | |
rsync -az -e ssh –delete ~/public_html/ remote.com:’~/public_html’ | Mirror web site (using compression and encryption) | |
rsync -auz -e ssh remote:/dir/ . && rsync -auz -e ssh . remote:/dir/ | Synchronize current directory with remote one | |
ssh $USER@$HOST command | Run command on $HOST as $USER (default command=shell) | |
* | ssh -f -Y $USER@$HOSTNAME xeyes | Run GUI command on $HOSTNAME as $USER |
scp -p -r $USER@$HOST: file dir/ | Copy with permissions to $USER’s home directory on $HOST | |
ssh -g -L 8080:localhost:80 root@$HOST | Forward connections to $HOSTNAME:8080 out to $HOST:80 | |
ssh -R 1434:imap:143 root@$HOST | Forward connections from $HOST:1434 in to imap:143 | |
* | (cd cmdline && wget -nd -pHEKk http://www.pixelbeat.org/cmdline.html) | Store local browsable version of a page to the current dir |
wget -c http://www.example.com/large.file | Continue downloading a partially downloaded file | |
wget -r -nd -np -l1 -A ‘*.jpg’ http://www.example.com/dir/ | Download a set of files to the current directory | |
wget ftp://remote/file[1-9].iso/ | FTP supports globbing directly | |
* | wget -q -O- http://www.pixelbeat.org/timeline.html | grep ‘a href’ | head | Process output directly |
echo ‘wget url’ | at 01:00 | Download url at 1AM to current dir | |
wget –limit-rate=20k url | Do a low priority download (limit to 20KB/s in this case) | |
wget -nv –spider –force-html -i bookmarks.html | Check links in a file | |
wget –mirror http://www.example.com/ | Efficiently update a local copy of a site (handy from cron) | |
ethtool eth0 | Show status of ethernet interface eth0 | |
ethtool –change eth0 autoneg off speed 100 duplex full | Manually set ethernet interface speed | |
iwconfig eth1 | Show status of wireless interface eth1 | |
iwconfig eth1 rate 1Mb/s fixed | Manually set wireless interface speed | |
* | iwlist scan | List wireless networks in range |
* | ip link show | List network interfaces |
ip link set dev eth0 name wan | Rename interface eth0 to wan | |
ip link set dev eth0 up | Bring interface eth0 up (or down) | |
* | ip addr show | List addresses for interfaces |
ip addr add 1.2.3.4/24 brd + dev eth0 | Add (or del) ip and mask (255.255.255.0) | |
* | ip route show | List routing table |
ip route add default via 1.2.3.254 | Set default gateway to 1.2.3.254 | |
* | tc qdisc add dev lo root handle 1:0 netem delay 20msec | Add 20ms latency to loopback device (for testing) |
* | tc qdisc del dev lo root | Remove latency added above |
* | host pixelbeat.org | Lookup DNS ip address for name or vice versa |
* | hostname -i | Lookup local ip address (equivalent to host `hostname`) |
* | whois pixelbeat.org | Lookup whois info for hostname or ip address |
* | netstat -tupl | List internet services on a system |
* | netstat -tup | List active connections to/from system |
* | smbtree | Find windows machines. See also findsmb |
nmblookup -A 1.2.3.4 | Find the windows (netbios) name associated with ip address | |
smbclient -L windows_box | List shares on windows machine or samba server | |
mount -t smbfs -o fmask=666,guest //windows_box/share /mnt/share | Mount a windows share | |
echo ‘message’ | smbclient -M windows_box | Send popup to windows machine (off by default in XP sp2) | |
sed ‘s/string1/string2/g’ | Replace string1 with string2 | |
sed ‘s/\(.*\)1/\12/g’ | Modify anystring1 to anystring2 | |
sed ‘/ *#/d; /^ *$/d’ | Remove comments and blank lines | |
sed ‘:a; /\\$/N; s/\\\n//; ta’ | Concatenate lines with trailing \ | |
sed ‘s/[ \t]*$//’ | Remove trailing spaces from lines | |
sed ‘s/\([\\`\\"$\\\\]\)/\\\1/g’ | Escape shell metacharacters active within double quotes | |
* | seq 10 | sed “s/^/ /; s/ *\(.\{7,\}\)/\1/” | Right align numbers |
sed -n ’1000p;1000q‘ | Print 1000th line | |
sed -n ’10,20p;20q‘ | Print lines 10 to 20 | |
sed -n ‘s/.* | Extract title from HTML web page | |
sort -t. -k1,1n -k2,2n -k3,3n -k4,4n | Sort IPV4 ip addresses | |
* | echo ‘Test’ | tr ‘[:lower:]‘ ‘[:upper:]‘ | Case conversion |
* | tr -dc ‘[:print:]‘ < /dev/urandom | Filter non printable characters |
* | history | wc -l | Count lines |
sort file1 file2 | uniq | Union of unsorted files | |
sort file1 file2 | uniq -d | Intersection of unsorted files | |
sort file1 file1 file2 | uniq -u | Difference of unsorted files | |
sort file1 file2 | uniq -u | Symmetric Differenceof unsorted files | |
join -a1 -a2 file1 file2 | Union of sorted files | |
join file1 file2 | Intersection of sorted files | |
join -v2 file1 file2 | Difference of sorted files | |
join -v1 -v2 file1 file2 | Symmetric Difference of sorted files | |
* | echo ‘(1 + sqrt(5))/2′ | bc -l | Quick math (Calculate Ï?). See also bc |
* | echo ‘pad=20; min=64; (100*10^6)/((pad+min)*8)’ | bc | More complex (int) e.g. This shows max FastE packet rate |
* | echo ‘pad=20; min=64; print (100E6)/((pad+min)*8)’ | python | Python handles scientific notation |
* | echo ‘pad=20; plot [64:1518] (100*10**6)/((pad+x)*8)’ | gnuplot -persist | Plot FastE packet rate vs packet size |
* | echo ‘obase=16; ibase=10; 64206′ | bc | Base conversion (decimal to hexadecimal) |
* | echo $((0x2dec)) | Base conversion (hex to dec) ((shell arithmetic expansion)) |
* | units -t ’100m/9.74s’ ‘miles/hour’ | Unit conversion (metric to imperial) |
* | units -t ’500GB’ ‘GiB’ | Unit conversion (SI toIEC prefixes) |
* | units -t ’1 googol’ | Definition lookup |
* | seq 100 | (tr ‘\n’ +; echo 0) | bc | Add a column of numbers. See alsoadd and funcpy |
* | cal -3 | Display a calendar |
* | cal 9 1752 | Display a calendar for a particular month year |
* | date -d fri | What date is it this friday. See also day |
* | date –date=’25 Dec’ +%A | What day does xmas fall on, this year |
* | date –date ’1970-01-01 UTC 2147483647 seconds’ | Convert number of seconds since the epoch to a date |
* | TZ=’:America/Los_Angeles’ date | What time is it on West coast of US (use tzselect to find TZ) |
echo “mail -s ‘get the train’P@draigBrady.com < /dev/null” | at 17:45 | Email reminder | |
* | echo “DISPLAY=$DISPLAY xmessage cooker” | at “NOW + 30 minutes” | Popup reminder |
* | printf “%’d\n” 1234 | Print number with thousands grouping appropriate to locale |
* | BLOCK_SIZE=\’1 ls -l | get ls to do thousands grouping appropriate to locale |
* | echo “I live in `locale territory`” | Extract info from locale database |
* | LANG=en_IE.utf8 locale int_prefix | Lookup locale info for specific country. See also ccodes |
* | locale | cut -d= -f1 | xargs locale -kc | less | List fields available in locale database |
* | recode -l | less | Show available conversions (aliases on each line) |
recode windows-1252.. file_to_change.txt | Windows “ansi” to local charset (auto does CRLF conversion) | |
recode utf-8/CRLF.. file_to_change.txt | Windows utf8 to local charset | |
recode iso-8859-15..utf8 file_to_change.txt | Latin9 (western europe) to utf8 | |
recode ../b64 < file.txt > file.b64 | Base64 encode | |
recode /qp.. < file.txt > file.qp | Quoted printable decode | |
recode ..HTML < file.txt > file.html | Text to HTML | |
* | recode -lf windows-1252 | grep euro | Lookup table of characters |
* | echo -n 0×80 | recode latin-9/x1..dump | Show what a code represents in latin-9 charmap |
* | echo -n 0x20AC | recode ucs-2/x2..latin-9/x | Show latin-9 encoding |
* | echo -n 0x20AC | recode ucs-2/x2..utf-8/x | Show utf-8 encoding |
gzip < /dev/cdrom > cdrom.iso.gz | Save copy of data cdrom | |
mkisofs -V LABEL -r dir | gzip > cdrom.iso.gz | Create cdrom image from contents of dir | |
mount -o loop cdrom.iso /mnt/dir | Mount the cdrom image at /mnt/dir (read only) | |
cdrecord -v dev=/dev/cdrom blank=fast | Clear a CDRW | |
gzip -dc cdrom.iso.gz | cdrecord -v dev=/dev/cdrom - | Burn cdrom image (use dev=ATAPI -scanbus to confirm dev) | |
cdparanoia -B | Rip audio tracks from CD to wav files in current dir | |
cdrecord -v dev=/dev/cdrom -audio *.wav | Make audio CD from all wavs in current dir (see also cdrdao) | |
oggenc –tracknum=’track’ track.cdda.wav -o ‘track.ogg’ | Make ogg file from wav file | |
* | ls -lSr | Show files by size, biggest last |
* | du -s * | sort -k1,1rn | head | Show top disk users in current dir. See also dutop |
* | df -h | Show free space on mounted filesystems |
* | df -i | Show free inodes on mounted filesystems |
* | fdisk -l | Show disks partitions sizes and types (run as root) |
* | rpm -q -a –qf ‘%10{SIZE}\t%{NAME}\n’ | sort -k1,1n | List all packages by installed size (Bytes) on rpm distros |
* | dpkg-query -W -f=’${Installed-Size;10}\t${Package}\n’ | sort -k1,1n | List all packages by installed size (KBytes) on deb distros |
* | dd bs=1 seek=2TB if=/dev/null of=ext3.test | Create a large test file (taking no space). See also truncate |
* | tail -f /var/log/messages | Monitor messages in a log file |
* | strace -c ls >/dev/null | Summarise/profile system calls made by command |
* | strace -f -e open ls >/dev/null | List system calls made by command |
* | ltrace -f -e getenv ls >/dev/null | List library calls made by command |
* | lsof -p $$ | List paths that process id has open |
* | lsof ~ | List processes that have specified path open |
* | tcpdump not port 22 | Show network traffic except ssh. See alsotcpdump_not_me |
* | ps -e -o pid,args –forest | List processes in a hierarchy |
* | ps -e -o pcpu,cpu,nice,state,cputime,args –sort pcpu | sed ‘/^ 0.0 /d’ | List processes by % cpu usage |
* | ps -e -orss=,args= | sort -b -k1,1n | pr -TW$COLUMNS | List processes by mem usage. See alsops_mem.py |
* | ps -C firefox-bin -L -o pid,tid,pcpu,state | List all threads for a particular process |
* | ps -p 1,2 | List info for particular process IDs |
* | last reboot | Show system reboot history |
* | free -m | Show amount of (remaining) RAM (-m displays in MB) |
* | watch -n1 ‘cat /proc/interrupts’ | Watch changeable data continuously |
* | uname -a | Show kernel version and system architecture |
* | head -n1 /etc/issue | Show name and version of distribution |
* | cat /proc/partitions | Show all partitions registered on the system |
* | grep MemTotal /proc/meminfo | Show RAM total seen by the system |
* | grep “model name” /proc/cpuinfo | Show CPU(s) info |
* | lspci -tv | Show PCI info |
* | lsusb -tv | Show USB info |
* | mount | column -t | List mounted filesystems on the system (and align output) |
# | dmidecode -q | less | Display SMBIOS/DMI information |
# | smartctl -A /dev/sda | grep Power_On_Hours | How long has this disk (system) been powered on in total |
# | hdparm -i /dev/sda | Show info about disk sda |
# | hdparm -tT /dev/sda | Do a read speed test on disk sda |
# | badblocks -s /dev/sda | Test for unreadable blocks on disk sda |
* | readline | Line editor used by bash, python, bc, gnuplot, … |
* | screen | Virtual terminals with detach capability, … |
* | mc | Powerful file manager that can browse rpm, tar, ftp, ssh, … |
* | gnuplot | Interactive/scriptable graphing |
* | links | Web browser |
* | alias hd=’od -Ax -tx1z -v’ | Handy hexdump. (usage e.g.: * hd /proc/self/cmdline | less) |
* | alias realpath=’readlink -f’ | Canonicalize path. (usage e.g.: * realpath ~/../$USER) |
* | set | grep $USER | Search currentenvironment |
touch -c -t 0304050607 file | Set file timestamp (YYMMDDhhmm) |
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