The Complete Class XI Notes — All In One Employability Skills · Information Technology (802) — Computer Organization · Networking & Internet · Relational DBMS with MySQL

Always say clearly what you want to say.

Always use simple language and say only what is required.

Always use proper words and phrases in the sentences.

Always use correct spelling and grammar in the sentences.

Your words should be related to the main topic and your words should make sense.

Your message should be complete and have all the needed information.

Be honest, respectful and friendly with others.

The movement and changes of the face are the facial expressions. Many times facial expressions show the feelings of a person. For example, expressing your thoughts using a smile — when we are happy, or when we are sad.

Posture means body positions. Posture shows how confident you are and your emotional feelings. For example, a straight body posture means confidence.

Gestures mean if you are sharing any idea or meaning with the help of your hands or head. For example, pointing, waving and using our hands when speaking.

Sometimes we communicate using touch; we also share messages with others through it, for example handshaking and patting on the back.

When two people are communicating you will find some space between these two people depending on the closeness or intimacy between them.

Maintaining eye contact is very important when you are talking about interest, whereas looking at any other side can make the other person feel ignored.

The tone of our voice, speed and volume that makes a difference in the meaning is a paralanguage.

Interests are the things that we enjoy doing.

An ability is an acquired or natural capacity that enables an individual to perform a particular task with considerable proficiency.

The act of putting on clothes is known as dressing.

Grooming is the act of making oneself appear neat, orderly and smart.

Always set your clear and specific goals.

A measurable goal answers the questions “How much?”, “How many?” and “How do I know that I have achieved results?”

Breaking down big goals into smaller parts will make the goal achievable.

A realistic goal would be something that we want to achieve and can work towards.

A goal should have a timeframe by when the goal needs to be achieved.

Data refers to raw facts or figures.

Processed data is called Information.

A set of instructions provided to the computer for doing a task is called a program.

Speed of processors is usually measured in megahertz (MHz) – millions of instructions per second; and gigahertz (GHz) – billions of instructions per second, is indicative of its power.

It is a common unit of measurement. It refers to the speed of communication over a data channel (or the speed with which information can be sent to and from a computer).

It is the ability of the computer to process data and instructions at very high speed. A typical high-speed computer performs 3 to 4 million instructions per second.

It is the ability of the computer to perform multiple tasks at the same time.

It performs 100% error-free calculations. The errors, if any, found in the output are either due to wrong entry of values or wrong instructions for computation. This phenomenon is often referred to as GIGO (Garbage In, Garbage Out).

It is the ability to perform tasks with the same speed and accuracy and does not suffer from human traits of tiredness and boredom.

It is the ability to store information for processing/future purposes.

Computers were merely dumb machines programmed to perform certain tasks. With the advent of artificial intelligence techniques, we now have machines that mimic human traits of decision making.

A device that helps the user to feed data, digits, commands etc.

A pointing device that helps the user to click and choose.

Microphone accepts sound in the form of analog signals, converts it to digital signals so that the computer can understand.

A scanner is an input device that scans documents such as photographs and pages of text. It creates an electronic version of the scanned document.

A barcode reader is an optical scanner that can read printed barcodes, decode the data contained in the barcode and send the data to a computer. The barcode uses lasers to identify the position and thickness of the bars.

A light-sensitive input device shaped like a pen allows the user to point to displayed objects or draw on the computer screen.

It displays the output to the user. The picture on a monitor is made up of thousands of tiny coloured dots called pixels.

The output is obtained as a hard copy, printed as characters/pictures on paper.

It converts the digital signals to analog form, in a format audible to the user.

Programmable read-only memory (PROM), or one-time programmable ROM (OTP), can be written or programmed via a special device called a PROM programmer. Once the chip has been programmed, the recorded information cannot be changed.

Erasable programmable read-only memory (EPROM) can be erased by exposure to strong ultraviolet light (typically for 10 minutes or longer) and can be reprogrammed to record different information using a special PROM program facility.

Electrically Erasable programmable read-only memory (EEPROM) is a type of ROM that can be programmed and erased by electrical signals. One of the new applications is the use of EEPROM as a backup to RAM memory whose contents are lost in a power failure. When power is returned, EEPROM memory can be used to replace the lost contents of the RAM memory and continue to work.

Hard disk stores information on one or more circular platters (disks) coated with magnetic material. The disks are stacked with space between them. Information is recorded on the surface of rotating disks by a magnetic head as tiny magnetic spots. Storage capacity is measured in gigabytes to terabytes.

The Compact Disc is an optical media, in which the information is stored and retrieved with the help of light. Storage capacity is up to 700 MB of data.

DVD is an optical storage device and can hold 4.7 GB (single layer, single-sided) up to 17 GB (dual layer, double-sided) of data. It is otherwise called Super Density Disc.

A pen drive is a portable storage device with solid-state memory, i.e. it has no moving parts unlike magnetic/optical media. It can be accessed by inserting it in the USB (Universal Serial Bus) port. Storage capacity goes up to 128 GB and beyond.

A Solid-State Drive (SSD) is a new generation storage device used in place of hard disks. There are no moving parts present in the SSD and it keeps the data safe.

Advantages: The SSD is lighter than a HDD and is resistant to shock and temperature changes · SSD produces less noise/heat because it uses computer chips and not moving parts · A solid-state drive consumes less power when compared to an HDD.

It is an optical storage device that stores huge amounts of data/high-definition video. The read/write operation is performed with a blue-violet laser. The storage capacity goes up to 128 GB of data.

Advantage of BD over CD/DVD: The BD uses a blue-violet laser (405 nm) that has a shorter wavelength compared to the red laser (650 nm) used in CD/DVD. Hence in BD it is possible to focus the laser spot with even greater precision, and it allows data to be packed more tightly in less space.

This is the main circuit board which holds together various components like CPU, memory, connectors for the hard drive and optical drives, expansion cards to control the video and audio, and connections in the form of various ports (such as USB ports). It provides connection to every component of the computer.

System bus is an electronic pathway of connecting cables that transmits data and instructions to the major components of a computer system.

Power Supply Unit converts alternate current power supply received by homes or offices to the low voltage direct current required by the machine.

It is an input device that captures data in the form of video/image.

Manages the communication needs of the system with the peripheral devices or the internet using special programs called drivers, which enable recognition of these devices and their properties.

The operating system handles the allocation of resources (memory, CPU time, files, secondary storage, input/output devices etc.) to the various processes to get an optimum performance from the system.

A process is a program currently getting executed in the memory or waiting for the CPU. The OS controls and manages multiple processes being executed in the computer.

The memory management component allocates Random Access Memory to the processes in a dynamic manner, that is, allocated on demand and released when not needed.

Operating system takes care of all the files and folders (directories) maintained on the computer disk. All the files stored in a computer system can be located through the file system.

A single-task OS allows execution of only a single program at any given instant. A multi-tasking OS can execute more than one program simultaneously; the processor time, in this case, is divided amongst various processes.

Single-user operating systems allow only one user to use the system. Desktop systems can be classified as typical single-user systems. Multi-user operating systems allow many users to access the system by maintaining an account of all the registered users.

They are intended for applications where data needs to be processed quickly, without any significant delays. For example, an anti-aircraft missile system must fire as soon as it receives a signal from the enemy aircraft.

In a batch processing system, similar jobs are clubbed together and submitted as a block to the processor for execution. User intervention is minimal in such systems. The jobs are picked up one by one and executed.

These tools help to manage data on disks for increased performance. It includes:
• Disk defragmenter – arranges files in contiguous memory locations and free space is consolidated to one contiguous block. It speeds up disk access and consolidates free space.
• Disk Cleanup – removes unwanted temporary files from the computer. It increases disk space and speed.
• Backup utility – helps to duplicate the disk information that can be used in case of data damage/loss.

It is used to compress large data files so that they take up less storage space. When needed, these compressed files can be exploded (extracted) back to the original form. Eg: WinRAR, PeaZip.

It scans the computer system for viruses (malicious program that disrupts normal functioning of the computer) and removes them. Eg: Kaspersky Antivirus.

• The system is in Sleep mode — click the mouse or press any key on the keyboard to wake it up.
• Check connection/power supply.

• Check connection of the mouse to the computer.
• Check for any damage (mouse/cable) – get it repaired or replaced.
• Clean the mouse.
• Check batteries in case of a wireless mouse.

• Check connection of the keyboard to the computer.
• Check for any damage – get it repaired or replaced.
• Clean the keyboard if the keys are stuck.
• Check batteries in case of a wireless keyboard.

• Check the cable connection.
• Check the volume level of the speakers. Click the Audio button in the Task Bar to make sure the sound is turned on and that the volume is up.
• Check audio player controls – many audio and video players have their own separate audio controls. Ensure that the sound is turned on and that the volume is set large enough to be heard.

Printer not responding:
• Printer is not connected properly or not switched on — Wired connection: check the cable connected to the printer; Wireless connection: check if the IP address configured on your computer matches the Dynamic IP address allocated to the printer.
• Printer is out of paper.
• Printer paper jam (paper is caught in the printer).
• Ink cartridge of the printer is empty.
• Update/Install printer driver.

When the computer becomes totally unresponsive — force a system restart. Press and hold the power button for 5–10 seconds to force the computer to shut down. Now switch on the computer again.

• Check for network connectivity.
• The Network card / Fly lead is not working properly.
• Run Windows Network Diagnostics – a troubleshooting application to diagnose and repair network problems (option available in Control Panel → Network and Sharing Centre).

• Open the Disk Cleanup app: Search → Disk Clean up
• Select the files to be deleted. Press OK.

• Open Network Sharing Center: Start button → Control Panel → Network and Sharing Centre
• The red cross (if found) between the USER-PC and Internet shows that the computer is not connected to the Internet.
• If not connected, the user can choose the required network and select connect.

• Open Command Prompt (type cmd in search).
• Type ping 127.0.0.1 and press Enter. If you get a reply, the network card is working.

• Open Command Prompt.
• Type IPCONFIG and press Enter. The result displays the Connection-specific IP Address if the system is connected to the internet, else Media State: Media disconnected.

The fly lead is the cable that connects the network card in your computer to a network point (usually on the wall). Check the cable if it is faulty or damaged by replacing it with a working cable.

• Open Network Sharing Center: Start → Control Panel → Network and Sharing Centre.
• Select Connect to a network option to view the available connections. Or click on the network icon on the Task bar to view available network connections.

• Open Printers & Scanners: Start → Control Panel → Printers & Scanners. It displays all the available printers.
• Choose the required printer to view the IP address.

• Click Start → All programs → Startups. It displays all the startup programs.
• Disable applications that are not required.

• Open Network Sharing Center: Start → Control Panel → Network and Sharing Centre.
• On the bottom-left corner of this screen, click the link Internet Options. This opens the Internet Properties dialog box.
• Select the General tab. Under Browsing History, check the Delete browsing history on exit checkbox, and then click the Delete button. This deletes the browsing history. Click OK to exit.

Reduce the printing quality by using Fast Draft / Fast Printing.

How do we remove temporary files?
Answer – To delete temporary files from the computer do the following –
Step 1: Click on Search
Step 2: Write %temp% and press enter
Step 3: Delete all files and folders

What could be the possible cause for all the applications to be running slow?
Answer – The possible causes for all the applications running slow are –
a. Viruses are affected in the computer
b. Free space on the hard drive – there should be at least 200–500 MB of free hard drive space on your system. Non-availability of free space slows the functioning of the computer.
c. Run a Disk Cleanup application
d. Delete unused files and programs
e. Empty your recycle bin
f. Remove temporary files

Describe the procedure to check whether the network card is working properly.
Answer – A working network card lights must be flashing or lit up. If there are no lights, it indicates either the network card is broken or there is no network to connect to. A broken network card needs repair or replacement.

How can we achieve disk defragmentation?
Answer –
• Open the Windows Explorer application and click on My Computer.
• Highlight the C drive and right click to get a pop-up menu.
• Select the Properties option from this popup menu.
• The dialog box showing the properties of the local disk (C:) is displayed.

What steps do you need to take to change the default printer?
Answer – To change the default printer, open the Devices and Printers dialog box. Choose the required printer and set it as the default printer.

What could be the reasons for the print jobs being sent to the wrong printer?
Answer – When there are multiple printers on a network, a possible problem could be that a print job is being sent to the wrong printer. This is because your system has set the default printer as Printer A, but you had wanted the print job to go to Printer B. You could either change the default printer to Printer B or choose Printer B for the current job.

ARPANET (Advanced Research Projects Agency Network) – the US Department of Defense (DoD) developed ARPANET in 1969 to connect geographically separated research computers together to form a network.

NSFNET (National Science Foundation Network) was developed in 1984 by NSF, U.S. for research and education purposes.

Internet Engineering Task Force.

Internet Corporation for Assigned Names and Numbers.

Internet Service Providers — they provide Internet connectivity for a fee.

A collection of interconnected nodes which communicate by means of some channel form a computer network.

The node that is responsible for sending the data.

The node that is responsible for receiving the data.

Message is the information or meaningful data that is being communicated in a structured form.

Channel is the communication medium through which the message is transmitted.

A repeater is a network device which is used to restore (reshape and amplify) the input signal to its original form so that it can travel a larger distance. It is also known as a digital generator. It is placed between two cable segments.

A hub is a central connection networking device that connects single nodes to form a network. It transmits data in the form of binary bits to all the other nodes in the network.

A switch is a central connection networking device that connects single node/segments of LAN to form a network. It transmits data in the form of frames only to the destination node in the network.

Similarity between Hub and Switch: all the nodes connected through a hub/switch form only one LAN.

The word "modem" stands for modulator-demodulator. A modem is used to send digital data over the phone line. It is an electronic device that converts Digital to analog signals (Modulation by the sending modem) and analog to Digital signals (Demodulation by the receiving modem) to transmit information over the network.

A bridge is a multiport device used for connecting two or more local area networks (LAN), possibly operating at different speeds. Thus, a bridge may be used to produce a bigger LAN by combining smaller LANs.

Routers are used for connecting various networks (LAN or WAN) with each other. A router maintains a routing table of various networks. It transmits data in the form of packets from an incoming network to the destination address in another network.

A gateway connects networks based on different protocol technologies to communicate with each other. Data coming from one network operating on one protocol is converted according to the protocol of the outgoing network, and then forwarded. A gateway is like a router equipped with software for protocol conversion.

A MAC (Media Access Control) address or Physical address is a unique 12-digit hexadecimal number assigned to each NIC by the manufacturer. The MAC address of an NIC is permanent and does not change.

By convention, MAC addresses are usually written in one of the following two formats:
MM:MM:MM:SS:SS:SS  OR  MM-MM-MM-SS-SS-SS

The first half (MM:MM:MM) of a MAC address contains the ID number of the adapter (NIC) manufacturer. The second half (SS:SS:SS) of a MAC address represents the serial number assigned to the adapter (NIC) by its manufacturer.

Eg: 00:A0:C9:14:C8:35 — 00:A0:C9 = ID number of the NIC manufacturer · 14:C8:35 = serial number assigned to the NIC by its manufacturer.

An IP address is a group of four bytes (or 32 bits) number, each of which can be a number from 0 to 255.

Eg: 59.177.134.72

IP addresses are normally expressed in decimal format as a "dotted decimal number". IP protocol identifies a machine with its IP address to route the packets in a network. The IP address assigned to the PC may change when it connects to the network next time.

A network protocol defines the rules and conventions of communication that must be followed when two devices interact with each other. It specifies what should be communicated, and how and when communication should take place.

Each resource on the internet has a unique address called URL (Uniform Resource Locator). URL is the address (location) of a website on a net server. e.g., http://www.microsoft.com

It is a collection of interrelated web pages hosted in a web server.

It is an electronic document that contains any type of information such as text, image, video, or sound in Web.

A software/program that helps us to navigate/view web pages.

A web server is a server that stores web documents and responds mainly to HTTP requests made by a web browser.

Digital literacy refers to raising knowledge and awareness about technology such as desktop computers, smartphones, tablets, and other electronic gadgets. It also includes familiarity with software tools and the internet.

Electronic mail or E-mail is a facility that allows users to send and receive messages across the Internet in a fast and secure manner. It allows us to attach files of other formats along with textual content.

To use the email facility, an email account is created with one of the mail servers (gmail, Yahoo mail, hotmail). Mail servers are computers that are dedicated to process and direct email.

E-mail addresses commonly take the form: username@hostname — an email address has two parts separated by the '@' ("at") symbol:
(i) Username – on the left side of the @ separator is the user name. A user name cannot have blanks.
(ii) Domain name – the portion to the right of @ indicates the host server / email service provider.
Eg. [email protected]

Email users: a sender is a person who sends the e-mail message and a receiver/recipient is a person who receives the message.

File Transfer Protocol is based on client-server architecture. Using FTP, local hosts (clients) can download or upload files to and from remote hosts (server).

Telnet stands for terminal network. It is a client-server-based application that allows the user working on one system to login and access a remote system.

Internet is a collection of computers or networking devices connected with the TCP/IP protocol. The World Wide Web is a collection of interlinked hypertext documents on the Internet using HTTP – Hypertext Transfer Protocol.

The TCP/IP (Transmission Control Protocol/Internet Protocol) is the glue which holds the Internet and WWW (collection of servers where information is stored) together.

TCP/IP protocols may be secured with cryptographic methods and security protocols like Secure Sockets Layer (SSL).

A firewall is a network security system that prevents unauthorized access to a network. In other words, it monitors and controls incoming and outgoing network traffic based on predetermined security rules.

Anti-virus is software that aims to protect your system against malicious and potentially unwanted programs. It scans the system to detect malicious programs, and removes or disables the program based on the settings.

A password manager is a software application that helps a user to store and organize passwords. Password managers usually store passwords encrypted, requiring the user to create a master password which grants the user access to their entire password database from top to bottom.

Cyber laws are the laws for systematic use of e-resources and serve as a measure against illegal cyber-crime. Various cyber laws have also been enacted to prevent cyber-crimes and take action against those involved in such crimes. These laws define the action that would be taken against people committing the offences. For cyber security, IT Act 2000 and the Information Technology Amendment Act, 2008 define offences and penalties for cyber-crime.

Create Database command creates a database, which acts as a container of tables.

CREATE DATABASE [IF NOT EXISTS] <database name>;

-- Example
CREATE DATABASE IF NOT EXISTS student;

The IF NOT EXISTS clause, if used, will first test whether a database by the mentioned name already exists or not. If it does, then the create database command is simply ignored, otherwise a database with the mentioned name is created.

The USE statement is used to select/open an already existing database on which the operations can be performed.

USE <database name>;

-- Example
USE student;

The SHOW DATABASES command displays the names of existing databases. To display specific databases, use the LIKE clause.

SHOW DATABASES;
SHOW DATABASES LIKE <database name>;

-- Example
SHOW DATABASES LIKE ‘student’;

DROP DATABASE is used to drop an existing database. It removes the database along with its contents.

DROP DATABASE <database name>;

-- Example
DROP DATABASE student;

DESCRIBE Table command allows the user to view the structure of an already created table.

DESCRIBE <tablename>;

-- Example
DESCRIBE student;   Or   DESC student;

Show tables command displays all the tables of the current database.

SHOW TABLES;

This statement is used to drop an existing table. When you use this statement, complete information present in the table will be lost.

DROP TABLE <table name>;

-- Example
DROP TABLE student;

The following syntax allows you to insert a new record with values on selected columns.

INSERT INTO <table name> [(<column list>)] VALUES (<value1>, <value2>, ……, <valuen>);

-- Schema: student (sno, name, address, phone, email)
INSERT INTO student(sno, name, phone) VALUES (1,’Arun’,7864532);

The following syntax allows you to insert a new record with values on all the columns.

INSERT INTO <table name> VALUES (<value1>, <value2>, …, <valuen>);

-- Schema: student (sno, name, address, phone, email)
INSERT INTO student VALUES (1,’Arun’, ‘P.BOX.NO.14, POSTAL CODE-516, Ibri’, 7864532, ’[email protected]’);

To insert NULL in a specific column, the word NULL can be inserted without quotes in the given column. NULL value indicates missing/unknown/not applicable value.

INSERT INTO student VALUES (1,’Arun’, ‘P.BOX.NO.14, POSTAL CODE-516, Ibri’, 7864532, NULL);

Date should be entered in the given format such as ‘YYYY-MM-DD’.

-- Schema: student (sno, name, address, phone, dob)
INSERT INTO student VALUES (1,’Arun’, ‘P.BOX.NO.14, POSTAL CODE-516, Ibri’, 7864532, ’1988-11-01’);

In SELECT command, either a complete list of all the columns or “*” should be specified to display all the columns in a table.

-- Query to display all the columns of salesman table
SELECT * FROM salesman;
-- or
SELECT salesman_id, name, city, commission FROM salesman;

In SELECT command, the column list of the required columns should be specified to display the required columns’ information.

-- Query to display name and commission of salesman table
SELECT name, commission FROM salesman;

SELECT command retrieves information based on the order of the columns specified by the user.

SELECT city, name, commission, salesman_id FROM salesman;

The DISTINCT keyword eliminates duplicate rows from the result of a SELECT statement.

SELECT DISTINCT(commission) FROM salesman;

The ALL keyword retains duplicate rows from the result of a SELECT statement. By default, SELECT command retains duplicate rows even if ALL is not specified.

SELECT ALL(commission) FROM salesman;

SELECT statement can be used to perform calculations and display the output. It can be used without the FROM clause as the computed values have no reference to any table.

SELECT 5+6;        -- Output: 11

MySQL provides a dummy small worktable called Dual, which has just one row and one column. It can be used for obtaining calculation results and system date.

SELECT 4*3 FROM dual;   -- Output: 12

The current date can be obtained using the curdate() function with the SELECT command.

SELECT curdate();      -- Output: 2020-11-10

SQL allows performing simple numeric computations by placing scalar expressions and constants along with the selected fields.

SELECT name, commission*100 FROM salesman;
-- Output columns:  name | commission*100

In a select query, the columns can be given different headings (column alias name) with the as keyword for output purposes. The column alias name having more than one word or special characters should be enclosed in quotation marks.

SELECT <column name> as [column alias], <column name> as [column alias]
FROM <tablename>;

-- Example
SELECT name as “salesman name”, city, commission*100 as com FROM salesman;
-- Output headings:  salesman name | city | com

In a select query, it is possible to insert text, enclosed within quotation marks, for output purposes. Text is inserted with the column names as per the requirement. The text makes the output more presentable, and it gets printed with every row of the output, not simply once for the table.

SELECT salesman_name, ’gets the commission’, comm.*100, ’%’ FROM salesman;

The BETWEEN operator defines a range of values that the column values must fall in, to make the condition True. The range includes both the lower value and the upper value. The operator NOT BETWEEN is the reverse of BETWEEN operator, that is, the rows not satisfying the BETWEEN condition are retrieved.

SELECT <column name> FROM <table name>
WHERE <column name> BETWEEN <lower value> AND <upper value>;

-- Query to list the items whose QOH falls between 30 to 50 (both inclusive)
SELECT Icode, Descp, QOH FROM Items WHERE QOH BETWEEN 30 AND 50;

IN operator is used to compare the given column against the specified list of values. It returns the record that matches a value in the given list of values. The NOT IN operator displays rows that do not match in the list.

SELECT <column names> FROM <table name>
WHERE <column name> IN (<value1>,<value2>,….<valuen>);

-- Schema: student (sname, city)
-- Query to return students from city ‘Delhi’, ‘Mumbai’ or ‘Kolkata’
SELECT * FROM student WHERE city IN (‘Delhi’,‘Mumbai’,‘Kolkata’);

LIKE is a string-matching operator that is used to compare character strings using patterns. Patterns are described using two special wildcard characters:
percent (%) – matches any substring.
underscore (_) – matches any single character.
Patterns are case-sensitive, that is, upper-case characters do not match lower-case characters, or vice-versa.

To illustrate pattern matching, consider the following examples:
• San% matches any string beginning with 'San'
• %idge% matches any string containing 'idge' as a substring, for example ‘Ridge’, ‘Bridges’, ‘Cartridge’, ‘Ridgeway’ etc.

SELECT <column names> FROM <table name> WHERE <column name> LIKE ‘<pattern string>’;

-- Schema: student (sname, marks, phoneno)
-- student name beginning with A as the first character
SELECT * FROM student WHERE sname LIKE ‘A%’;
-- student name ending with s as the last character
SELECT name FROM student WHERE name LIKE ‘%s’;
-- student name with b as the second character
SELECT name FROM student WHERE name LIKE ‘_b%’;

In a select query, the IS NULL operator is used in the WHERE clause to check for empty values (NULL values). It returns the records that contain NULL in the given column.

SELECT <column names> FROM <table name> WHERE <column name> IS NULL;

-- pet table
SELECT name, birth, death FROM pet WHERE death IS NULL;

In a select query, the IS NOT NULL operator is used in the WHERE clause to check for values other than NULL. It returns the records that contain values other than NULL in the given column.

SELECT <column names> FROM <table name> WHERE <column name> IS NOT NULL;

-- pet table
SELECT name, birth, death FROM pet WHERE death IS NOT NULL;

Update command is used to modify the values of one or more records in the table.

UPDATE <tablename>
SET Column1 = Value1 [, Column2 = Value2, ..]
WHERE <Condition>;

The WHERE clause in an UPDATE command updates the selected records based on the condition. If omitted, ALL records will be updated!

-- Eg 1: To update English marks of ALL the students to 100 in student table
UPDATE student SET english=100;

-- Eg 2: To update english marks of Arun and David to 100
UPDATE student SET english=100 WHERE sname='Arun' or sname='David';

Delete command is used to delete one or more records from the given table. The WHERE clause in a DELETE query deletes selected records based on the condition; if omitted all the records would be deleted.

DELETE FROM <tablename> WHERE <Condition>;

-- Eg-1: To delete student records with sno < 12
DELETE FROM student WHERE sno<12;

-- Eg-2: To delete ALL the records of student table
DELETE FROM student;