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What is SQL Injection?

SQL injection is a security flaw that grants an intruder access to add, delete, or modify the application’s database and queries. 

For instance, in November, a SQL injection was found in the Zendesk CRM by a few Varonis Threat Labs researchers. Due to the vulnerability, the intruder would have had access to over 100,000 customer data. The issue was, however, resolved within a week with the help of those researchers.

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Key Highlights

SQL injection or SQLi is a popular attack method that uses malicious SQL code to manipulate backend databases and access secure data.

There are three types of SQLi options: in-band, inferential, and out-of-band.

Intruders use SQL queries and commands like data retrieval, update, removal, and modification to carry out these attacks.

The SELECT statement is the most popular and common option to detect vulnerabilities.

How to Create an SQL Statement?

A structured query is used to accomplish an SQL statement by triggering the desired answer. The attacker needs the response to comprehend the database design and gain access to the application’s safeguarded data. SQL injection can be carried out by an attacker using the following techniques:

1: A Constant True SQL Statement

A hacker uses a SQL statement that is perpetually true to carry out a SQL injection.

As an illustration, the hacker chooses 1=1 rather than just inputting the “false” data because it is a statement that is always true.

2: Batched SQL Injection

A group of SQL statements are combined into a batch SQL injection and are separated by semicolons.

However, it must be kept in mind that if the SQL commands (the statement that appears after the semicolon) are legitimate, this strategy can function properly.

Real-Life Examples Example #1: GhostShell Attack

The most renowned cyber attack by the Ghost gang was taken over, where they claimed to leak around million user accounts from 100 websites worldwide. Their main targets were government agencies, banks, manufacturing companies, and banks. The attackers employed the famous SQLmap tool for this attack and hacked databases that included around 30,000 records.

Example #2: 7-Eleven Breach

On August 8, 2023, a group of hackers attacked the retail chain of 7-Eleven, where they stole 130 million credit card numbers. It was confirmed that each customer loses around $600 million and the hackers did this via the newly launched payment app of the store, i.e., 7pay. After this incident, the store was closed for a long time, and people were instructed to block their cards.

Example #3: HBGary Breach More Examples Example #1

Say you have entered “100 OR 1=1” when submitting the query. The response that it will return will be in the table details.

“OR” “=”

You certainly notice a similarity with the above SQL injection method. An attacker will insert “OR” “=” in the query box. It is a malicious code and will dig deeper into the application.

Example #2

A hacker wants to retrieve a user’s login ID and password from the SQL database.  The hacker will type “OR=” in the user ID and password section. Since this is a valid SQL statement, the hacker will have access to the user ID and password without any trouble.

Example #3 How to Detect Vulnerabilities?

There are three types of queries available to detect SQL Injection.

#1 SELECT statement

The Select Query statement fetches specific information or data from the database.

If you want to retrieve data from the SQL database, you must use the SELECT statement.

One uses the SELECT statement commonly for information search purposes or to view a specific profile in a table.

In some scenarios, one uses the SELECT statement for login purposes.

#2 INSERT statement

The Insert Query statement is used to insert data or info into the database.

If you want to include a new row in the database table, you need to use the INSERT command. They are frequently used whenever a program makes a new order, includes new data in the audit log, or creates a new account for the user.

If you are creating a new user account, you need to use the INSERT statement to submit the data into the database.

The syntax:

INSERT INTO accounts (user_name, password, signature) VALUES (‘xxx,’ ‘yyy,’ ‘zzz’);

Mention the account’s name in the “accounts” section and observe the “(user_name, password, signature)” section of the syntax.

These are the names of the columns featured in the database. If the database does not feature the columns’ names, you need to add them.

Move to the section that precedes VALUES, “(‘xxx,’ ‘yyy,’ ‘zzz’)” and insert the username for ‘xxx,’ password for ‘yyy,’ and a signature for ‘zzz.’

Due to the high risk, keeping the application secured is important. It can be hacked by specially designed input and injecting random values in the  database.

Use the user_name parameter: (‘name,” pass,” sign’)- to examine the vulnerability of the data.

After finding the location of the injected data in the database, it becomes easy to modify the data or even extract it by altering the input.

#3 UPDATE statement

The Update Query statement is used to alter or modify the content of the database.

One uses the UPDATE statement to manage the proceedings if one wants to alter the existing rows in a database table.

One uses the UPDATE statement commonly to modify passwords, change the value quality on a line, or even update contact details.

The UPDATE statement is very similar to that of the INSERT statement but with a slight difference, the use of the WHERE clause that indicates the rows in the table to be updated.

For example, UPDATE Contacts SET Phone Number=”569853264″ WHERE Name = ‘Sandy’

Types of SQL Injections #1 In-band SQLi

The attack and the resulting gathering are made using the same communication channel for the attacker. One of the most prevalent kinds of SQLi attacks is the in-band SQLi due to its simplicity and effectiveness.

Error-Based Injection

In this type of injection, the hacker will try to insert a spam query into the table’s fields, and the output will display an error, indicating a problem in the database or SQL syntax.

This technique is considered the simplest and easiest of the two to detect the location of the SQL injection.

Union Based Injection

This method uses the SQL operator UNION, which combines many select statements produced by the database into one HTTP response.

The information in this response might be useful to the attacker.

#2 Inferential SQLi

Also known as Blind Based Injection, the hacker injects the malicious syntax or query into the SQL database table. Here, the output message will only indicate that the syntax is incorrect. Through this approach, the hacker will try to retrieve some information by verifying true or false statements when querying.


The attacker issues a query to the SQL database to force the application to deliver a result. Based on the pattern of the inquiry (true or false), the outcome will change.

Depending on the outcome, the data in the response server will change or remain the same. After then, the attacker can determine whether the output is true or false.

The database must wait (for a time in seconds) before responding to the attacker’s SQL query, which is sent to the database. Depending on how long it takes the database to answer, an attacker can determine the validity of the query.

Depending on the outcome, an HTTP reply will either be generated immediately or after a short delay. Thus, the attacker does not need to rely on information from the database to determine whether the message returned true or false.

#3 Out-of-band SQLi

Out-of-band SQLi is carried out when a hacker cannot utilize the same channel to retrieve information or attack the server.

One can also use it with slow and unstable servers.

These strategies rely on the server’s ability to send HTTP and DNS requests to send data to an intruder.

How to Prevent SQL Injection?

The user/developer needs to filter every input from the program, including single quotes (likely to hold malicious elements), as well as login forms and other web input forms.

Next, turning off the database error visibility on the site is a better idea to prevent further damage.

Remember, database errors can prove harmful in giving away information regarding the database.

One uses WAF, or Web Application Firewall, to eradicate online threats and filter out SQL injection attacks. It first detects a suspicious input. Then it cross-verifies the same with the concerned IP data before deciding whether it’s malicious, and then the IP can only block the input if it has a bad user interface.

Final Thoughts

Although SQL injection is primarily recognized as a website attack vector, it may be used to target any kind of SQL database. When it comes to vulnerabilities in SQL databases, detecting them is of real importance. Without detecting the vulnerabilities in the database, it will become impossible to move on with the identification process.

Frequently Asked Questions (FAQs) Q1. What is an injection in SQL?

Answer: SQL injection is known as a code injection technique that might corrupt or destroy any database. It is one of the most commonly used web hacking techniques used by hackers. In this entire process, the hacker places malicious code in the SQL statements through web page input.

Q2. What are the three types of SQL injection?

Answer: Typically, SQL injection is divided into three categories: In-band SQLi (Classic), Inferential SQLi (Blind), and Out-of-band SQLi. One can classify the types of SQL injections on the basis of methods used to gain access to backend data and the potential damage.

Q3. What can a hacker do with the SQL injection process?

Answer: The potential outcomes if the application has a SQL injection vulnerability include Possible authentication bypass, the confidentiality of the data could be compromised, and an attacker can modify and delete database data and remove entries.

Q4. Which tool is best for SQL injection?

Answer: SQLMAP is an open-source SQL injection tool and is popularly used SQL injection amongst folks. This tool helps to make it very easy to exploit the SQL injection vulnerabilities of any web application and gain access to the database server.

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Basic Sql Injection And Mitigation With Example

SQL injection is a type of cyber attack that allows attackers to execute malicious SQL statements on a database. These statements can be used to manipulate data, retrieve sensitive information, or even delete entire databases. It is one of the most common and dangerous types of web vulnerabilities, and it can affect any website or web application that uses a SQL database.

In this article, we will cover the basics of SQL injection, how it works, and how to prevent it. We will also provide an example of a basic SQL injection attack and show how to mitigate it.

What is SQL Injection?

SQL, or Structured Query Language, is a programming language used to manage and manipulate data stored in relational databases. It is the standard language for interacting with databases, and it is used by millions of websites and applications around the world.

SQL injection is a type of cyber attack that exploits vulnerabilities in SQL-based applications. It allows attackers to insert malicious code into an application’s SQL statements, which can then be executed by the database. This can allow attackers to gain unauthorized access to sensitive data, modify or delete data, and even gain control of the entire database.

How Does SQL Injection Work?

For example, consider a simple login form that asks for a username and password. The application might generate an SQL query like this to verify the user’s credentials &miuns;

SELECT * FROM users WHERE username='$username' AND password='$password';

In this case, the $username and $password variables are replaced with the user’s input. If a user enters their own username and password, the query will work as intended. However, if an attacker enters malicious input, they can manipulate the query to do things like retrieve sensitive data or even delete entire tables.

For example, an attacker might enter the following as their password −

' OR 1=1; - SELECT * FROM users WHERE username='$username' AND password='' OR 1=1; --'; How to Prevent SQL Injection?

Preventing SQL injection attacks requires a combination of good design practices and proper input validation. Here are a few steps you can take to protect your application −

Use parameterized queries − One of the easiest and most effective ways to prevent SQL injection is to use parameterized queries. This involves separating the SQL code from the user input and passing the input as a separate parameter. This ensures that the input is treated as a value, rather than part of the SQL code, and makes it much harder for attackers to inject malicious code.

Validate and sanitize user input − Another important step is to validate and sanitize all user input. This involves checking the input for any characters or patterns that might indicate an attempt to inject malicious code. You should also limit the type and length of input that users can enter.

Use prepared statements − Prepared statements are a type of parameterized query that can be used to protect against SQL injection. They allow you to create a template for an SQL statement, and then pass in the parameters at a later time. This can help to prevent SQL injection because the parameters are not parsed until they are passed to the prepared statement, which means that any malicious code will be treated as a value, rather than part of the SQL code.

Enforce strong passwords − One of the most common ways for attackers to gain access to a database is by guessing or cracking weak passwords. To prevent this, you should enforce strong password policies, including using long passwords that are difficult to guess or crack. You should also consider using two-factor authentication or other security measures to protect sensitive accounts.

Example: Basic SQL Injection Attack and Mitigation

To illustrate the basics of SQL injection, let’s walk through an example of a simple login form that is vulnerable to injection attacks. We will then show how to mitigate the vulnerability using parameterized queries.

First, let’s create a simple table in a MySQL database to hold our users −























Next, let’s create a login form with a simple HTML form −


The form sends a POST request to chúng tôi with the username and password fields. We can then use PHP to handle the request and check the user’s credentials against the database −



















































"SELECT * FROM users WHERE username='


' AND password='





"Logged in successfully!"






"Invalid username or password"




This code creates an SQL query using the `username` and `password` fields from the form, and then executes the query using the `query()` method of the ‘mysqli’ object. If the query returns any rows, it means that the username and password are correct, and the user is logged in.

However, this code is vulnerable to SQL injection attacks. An attacker can enter malicious input into the form, which will be incorporated directly into the SQL query. For example, if an attacker enters the following as their username −

admin' --

The resulting SQL query will look like this −

SELECT * FROM users WHERE username='admin' --' AND password='$password';


















































"Logged in successfully!"






"Invalid username or password"




In this version of the code, we use a prepared statement to create a template for the SQL query. We then bind the username and password variables to the prepared statement as parameters, using the bind_param() method. This ensures that the input is treated as a value, rather than part of the SQL code, which makes it much harder for attackers to inject malicious code.


SQL injection is a serious and widespread security vulnerability that can compromise the integrity and confidentiality of your database. To protect your applications and your data, it is important to follow best practices for designing and implementing your SQL code, and to use proper input validation and sanitization techniques. By using parameterized queries and other prevention measures, you can help to prevent SQL injection attacks and keep your applications and data safe.

Learn 7 Most Useful Types Of Keys In Sql

Introduction to SQL Keys

In SQL, keys are the set of attributes that used to identify the specific row in a table and to find or create the relation between two or more tables i.e keys identify the rows by combining one or more columns. SQL provides super key, primary key, candidate key, alternate key, foreign key, compound key, composite key, and surrogate key. SQL keys use constraints to uniquely identify rows from karger data.

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CREATE TABLE `customer` ( `cust_id` int(11) NOT NULL, `cust_name` varchar(100) NOT NULL, `cust_address` text NOT NULL, `cust_aadhaar_number` varchar(50) DEFAULT NULL, `cust_pan_number` varchar(50) NOT NULL ) ENGINE=InnoDB DEFAULT CHARSET=latin1; ALTER TABLE `customer` ADD PRIMARY KEY (`cust_id`);

In the above-given SQL query, we can see how a column ‘cust_id’ is set as a Primary Key.

Type of SQL Keys

Multiple types of Keys are supported by the SQL Server.

The following are the list of SQL Keys:

Primary Key

Unique Key

Candidate Key

Alternate Key

Composite Key

Super Key

Foreign Key

For Example 

Customer Table

cust_id cust_name cust_address cust_aadhaar_number cust_pan_number

100001 Sunil Kumar Noida 372464389211 ADSFS3456K

100002 Ankit Gupta Gr Noida 442289458453 CGHAD7583L

100003 Suresh Yadav New Delhi 878453444144 NMKRT2278O

100004 Nilam Singh Lucknow 227643441123 HFJFD3876U

100005 Amal Rawat Ghaziabad 932571156735 CBMVA9734A

100006 Harsh Saxena Kanpur 1453534363319 TRYUC2568H

Below given the “Order” table having the related data corresponding to the “cust_id” from the Customer Table.

Order Table

cust_id order_month_year order_amount

100001 2024 – Jan $100,000

100002 2024 – Jan $120,000

100003 2024 – Jan $100,000

100004 2024 – Jan $110,000

100001 2024 – Feb $105,000

100002 2024 – Feb $125,000

Now, we will go through one by one on each of the Key:

1. Primary Key

Primary Key is a field that can be used to identify all the tuples uniquely in the database. Only one of the columns can be declared as a primary key. A Primary Key can not have a NULL value.

Example: In the above given relational table, “cust_id” is the Primary Key as it can identify all the row uniquely from the table.

2. Unique Key

Unique Key can be a field or set of fields that can be used to uniquely identify the tuple from the database. One or more fields can be declared as a unique Key. The unique Key column can also hold the NULL value. Use of Unique Key improves the performance of data retrieval. It makes searching for records from the database much more faster & efficient.

Example: In the above given relational table, “cust_aadhaar_number”, “cust_pan_number” are the Unique Key as it can allow one value as a NULL in the column

3. Candidate Key

Candidate Key can be a column or group of columns that can qualify for the Unique Key. Every table has at least one Candidate Key. A table may have one or more Candidate Key. Each Candidate Key can work as a Primary Key if required in certain scenarios.

Example: In the above given relational table, “cust_id”, “cust_aadhaar_number”, “cust_pan_number” are the Candidate Key as it can identify all the row uniquely from the table. These columns also qualify the criteria to be a Primary Key.

 4. Alternate Key

Alternate Key is that Key which can be used as a Primary Key if required. Alternate Key also qualifies to be a Primary Key but for the time being, It is not the Primary Key.

Example: In the above given relational table, “cust_aadhaar_number”, “cust_pan_number” are the Alternate Key as both of the columns can be a Primary Key but not yet selected for the Primary Key.

5. Composite Key

Composite Key is also known as Compound Key / Concatenated Key. Composite Key refers to a group of two or more columns that can be used to identify a tuple from the table uniquely. A group of the column in combination with each other can identify a row uniquely but a single column of that group doesn’t promise to identify the row uniquely.

Example: In the above given relational table i.e. Order Table, “cust_id”, “order_month_year” group of these columns used in combination to identify the tuple uniquely in the Order Table. The individual column of this table is not able to identify the tuple uniquely from the Order table.

6. Super Key

Example: In the above given relational table, Primary Key, Candidate Key & Unique Key is the Super Key. As a single column of Customer Table i.e ‘cust_id’ is sufficient to identify the tuples uniquely from the table. Any set of the column which contains ‘cust_aadhaar_number’, ‘cust_pan_number’ is a Super Key.

7. Foreign Key

A foreign key is a column which is known as Primary Key in the other table i.e. A Primary Key in a table can be referred to as a Foreign Key in another table. Foreign Key may have duplicate & NULL values if it is defined to accept NULL values.

Example: In the above given relational table, ‘cust_id’ is Primary Key in the Customer table but ‘cust_id’ in the Order table known as a ‘Foreign Key’. Foreign Key in a table always becomes the Primary Key on the other table.

The above-given picture displays how each column is shown as a Key according to their qualification to identify the tuples uniquely from the table. Screenshot summarizes all the Key through the use of the relational table.


SQL Keys is one of the attributes of the relational database. which plays important roles to establish a relationship between two or more tables. It also helps queries to execute faster i.e. retrieval of the records from the database becomes much faster by using Keys. Keys also set the different constraint to uniquely identify the tuples from the large data.

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This is a guide to SQL Keys. Here we discuss the introduction to SQL Keys and 7 different types with the appropriate example in detail. You may also look at the following article –

What Is Adhoc Testing? (Types, Examples)

Adhoc testing is frequently carried out to break the system in unusual ways. Adhoc testing’s most remarkable aspect is that it lacks any test design approach for creating test cases.

The procedure is generally used to identify software flaws. Because adhoc testing lacks test cases, it is often carried out without documentation.

Take a closer look at the procedure. Ad-Hoc testing is a kind of testing that comes under the category of ‘Unstructured Testing.’

Structured Testing Vs. Unstructured Testing

StructuredTesting − Everything that happens throughout the testing method, from the development of test cases to their sequential execution, is written in this technique. This script is followed by the testers while doing tests.

Unstructured Testing − Testing is typically done by error guessing in this technique, where the testers construct the test cases throughout the testing process.

Adhoc Testing

Adhoc testing is a term that refers to testing that is done on the fly. It is a form of unstructured testing technique, as described above, in which no systematic strategy is made before the testing process begins. As a result, no requirement specification or test case preparation and design is done prior to testing.

Ad-hoc testing is generally carried out by a tester who is well-versed in the program under test, both in terms of what it does and how it works. This testing is carried out by constructing test cases at random using error guessing and running them without regard for any test criteria.

Finding possible regions of the program where mistakes may exist is an important aspect of this testing. Because of this, it’s also known as Monkey Testing or Random Testing. As a result, only those testers with a thorough understanding of the product should execute this test.

Ad-Hoc testing has the benefit of saving time that would otherwise be spent on documents such as test requirements, test case planning, design, and so on. It is also often done after the structured testing has been completed. This is done in order to uncover software problems that would not have been found by following the previously prepared test cases.

Adhoc Testing Types

Following are some of the types of Adhoc Testing −

Buddy Testing

Monkey Testing

Pair Testing

Buddy Testing

In this sort of Ad-Hoc testing, at least two individuals work together to conduct the tests. At least one software tester and one software developer normally make up this team.

This sort of testing occurs after the unit testing of a module has been finished.

On that module, the two ‘buddies’ collaborate to develop legitimate test cases.

This is done to ensure that the tester does not report problems caused by incorrect test cases. This form of testing may also be thought of as a hybrid of unit and system testing.

Monkey Testing

The term ‘monkey testing’ refers to the unpredictability of the technique utilized in this testing.

Random inputs are presented to the program under test, and their associated outputs are monitored.

Any occurrences of errors, inconsistencies, or system failures are identified based on the acquired outputs.

Pair Testing

This kind of testing is similar to buddy testing. In this case, however, just a couple of testers collaborate on the modules for testing.

They collaborate to uncover faults and problems by sharing ideas, views, and expertise on the same computer.

To acquire a distinct perspective on each issue, testers are partnered according to their knowledge levels and experience.

Adhoc Testing Characteristics

This testing occurs after the program has been subjected to formal testing methodologies. The reason for this is because ad-hoc tests are performed to discover application abnormalities that cannot be foreseen prior to testing.

This testing can only be carried out by testers who have a deep understanding of how the program works. Because good ‘error guessing’ can only be done when the tester understands what the program does and how it operates, this is the case.

The Ad-hoc testing approach is best for detecting defects and inconsistencies in an application that lead to serious gaps. Errors like this are often difficult to spot.

This kind of testing requires less time than other types of testing. This is due to the fact that it is carried out without any previous planning, design, or structure.

Ad-hoc testing is done just once since any faults discovered need retesting.

Adhoc Tests Examples

Testing an application’s functionality when the browser settings are altered. Identifying faults that occur when the JavaScript option is deactivated in various browsers, for example.

Putting the app through its paces on several platforms. It’s critical to test if the produced application runs smoothly across a variety of operating systems and browsers.

Providing inputs to the system that are outside of the valid-inputs range in order to see whether the application’s response is adequate.

Copying and modifying the application’s URL to make it run in a different browser. This is done to ensure that unauthenticated access to the system is not granted to any unauthorized users.

Going through a series of random actions or traveling around the program at random in order to verify the outcomes achieved by using a certain combination of odd inputs.

When Should Adhoc Testing Be Conducted?

When there isn’t enough time to complete extensive and thorough testing, which involves producing test requirements documents, test cases, and test case designs, ad-hoc testing is usually used. Following the completion of formal testing methodologies is the ideal time to undertake this sort of testing.

Ad-hoc testing, on the other hand, may be carried out in the midst of software development. It may be done after the program has been completely created, or even after just a few modules have been produced. It may also be carried out as part of the official testing procedure. However, there are a few instances in which this testing is not required. As a result, every tester must be aware of when to avoid this kind of testing.

The following are some examples of why ad-hoc testing should not be done −

When Beta testing is in progress, no ad hoc testing should be done. This is due to the fact that beta testing entails customers evaluating the generated software in order to make ideas for new features that should be included or to modify the requirements for it.

It is also recommended that this testing not be carried out in test cases that already include problems. Before the mistakes can be deleted from the system, they must first be properly recorded. The test cases must be retested once they have been fixed to confirm that they are operating properly.

What Benefits Does Adhoc Testing Offer?

Many mistakes that go undiscovered when just formal testing techniques are employed may be uncovered by randomly testing the program, which is one benefit of ad-hoc testing.

The testers are allowed to explore the program as they see fit, based on their intuition and comprehension of it. They may then run the tests as they proceed, assisting them in identifying mistakes as they go.

The application can be simply tested by both testers and developers since no test cases need to be prepared and built. This makes it easier for developers to write more effective and error-free code.

This testing may also aid in the construction of one-of-a-kind test scenarios that can discover problems ineffectively. As a result, such test cases may be combined with other scheduled test cases in formal testing.

Because there is no formal method for ad-hoc testing, it may be done at any point throughout the software development lifecycle.

It may be used in conjunction with other testing methods to create more informed and effective findings.

Drawbacks of Ad hoc Testing

It’s difficult for the tester to recreate an issue since the testing method isn’t defined and no specific test case is performed. This is because the tester must recall the precise procedures he took to get the mistake, which is not always achievable.

Erroneous errors are sometimes reported as a result of the tester randomly executing invalid test cases, which causes a problem in the following error correcting operations.

Ad-hoc testing will not be able to find any mistakes if the testers do not have previous knowledge of the workings of the application under test. This is due to the fact that testers must work through error guessing and construct and run test cases on the fly.

Ad-hoc testing does not guarantee that faults will be discovered. Proactive error guessing for testing is entirely dependent on the tester’s competence and expertise.

The amount of time and effort that goes into this testing is unknown since there are no previously established and documented test cases. Finding even a single mistake might take a long time in certain cases.

Conducting Adhoc Testing: Best Practices

It’s critical to understand the most effective and efficient methods to use the Ad-Hoc testing methodology in order to perform it properly. This is because if tests are not completed properly, the time and effort invested in them would be squandered. As a result, in order to undertake this sort of testing, one must be aware of the best practices that may aid in a more complete testing approach −

Expertise in Software

Ascertain that the tester assigned to the application’s ad-hoc testing has a thorough understanding of the application.

To support better ‘error guessing’ on the application, the tester must be conversant with all of the program’s capabilities.

Finding more mistakes, flaws, and inconsistencies becomes simpler with enough information to back up the tester’s testing method.

Identify Potentially Error-Prone Areas

If testers are unfamiliar with the program, the best approach is for them to begin their testing by looking for the section of the application where the most of the mistakes occur.

Selecting such sensitive locations for ad-hoc testing may aid in the detection of problems.

Determine which areas of the test should be prioritized.

It is best to begin testing with the portions of the program that are most often utilized by end-users or customers. This aids in the protection of critical features and the early detection of any bugs.

Make a rough plan for the test.

Although adhoc testing does not need any previous preparation or documentation, a basic strategy may be highly beneficial and efficient. Simply noting the important points and locations that need to be tested will assist the testers in covering most of the program in the shortest period of time.


To make testing easier, you’ll need the necessary tools such as debuggers, task monitors, and profilers.

What Is Duopoly? Types, Examples, Characteristics, Pros & Cons

What is Duopoly?

In a monopoly, a single player dominates the market for a particular product. In contrast, in a duopoly, two players have a clear dominance for a specific product. The two players compete with each other to increase their market share and often serve a loyal customer base of their own.

Key Highlights

A duopoly is where two companies hold a majority, i.e., 50% or more of the market share.

The two companies are interdependent while enjoying a monopoly for their loyal base of customers.

It is of two types: Cournot, and Bertrand, based on what triggers the competition between the two companies.

There are various real-life examples like Apple, Samsung, Airbus, and Boeing.

How Does it Work?

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The producer from two companies dominates in a Duopoly, a particular product in a market sector. In this condition, various companies compete with each other by lowering the prices of their products. This situation benefits the consumers.

Even though there will only be two competitors in the market, with the mutual acceptance between these two companies, it can become a monopoly. A monopoly is a condition in which a single producer of the product in the market will exist.

Types Cournot

According to this, the volume of goods or services produced decides the competition between the two players.

The two companies produce their goods to maximize profits. Thus, in the long run, an equilibrium is set for both companies in terms of output.

Hence, there is no incentive to start a price war. There is no collusion between the companies, and each company produces to maximize its profit.


In this market, price competition exists between two firms, and customers opting for the lowest prices can create a price war.

The two firms implement low pricing strategies leading to their depleting profits.

In this, customers enjoy purchasing goods and services at low prices while profits for companies dwindle due to existing competition.

Examples Boeing and Airbus

Boeing and Airbus have been considered duopolies in the large jet airplane manufacturing market since 1990.

Together, they own nearly 90% of the market share of airplane manufacturing.

The creation of Airbus made airplane manufacturing more competitive, forcing Boeing to be more price competitive and present an excellent service.

Apple and Samsung

Apple and Samsung companies combined to dominate the smartphone market.

The remaining smartphone manufacturers contribute less than 25% of the smartphone industry.

Visa and Mastercard

Visa and Mastercard are considered Duopoly in card payment services.

Of all the card transactions in European countries, 80% are through Visa and Master cards.

Coca-Cola and Pepsi

Another example is in the beverage industry, where Coca-Cola and Pepsi dominate.

Coca-Cola has a 43% market share, while Pepsi has 29% giving both companies a concentration of more than 70% in the cola market.

While both players spend a fortune to promote their brands, they do not launch a campaign against each other as it may be mutually harmful, as seen in their earlier campaigns in the 1970s.


The two big players affect each other’s decisions.

The change in the price of the product by one player will also influence the pricing strategy of another player.

Similarly, launching a different quality product within the same niche will force another player to launch a similar product to stay competitive.

As there are only two players for the majority market share, each player develops a loyal customer base over time. Hence, they enjoy significant individual monopoly powers. For example, Samsung and Apple have developed a substantial, loyal customer base, and now Apple enjoys a monopoly for its market share of customers.

The two players avoid head-to-head competition as it is mutually harmful.

The duopolies are neither compatible nor conflicting and tend to focus on their work to win the market share.

How is Duopsony Different from Duopoly?



Duopsony is an economic condition with only prominent buyers for a particular product or service. Two big players have more than 70% market share for the supply of the product.

Duopsony is also called buyer’s Duopoly and is a category of an oligopsony. It is a form of oligopoly.

For example, Intel Corporation and Advanced Micro Devices Inc are the leading manufacturers of microchips. For example, Flipkart and Amazon are leading e-commerce companies.

Companies benefit by cooperating. It limits free trade.

The two companies collude to decide upon a rate that maintains demand equilibrium and maximizes profits without competitors.

Companies concentrate on improving the quality of their existing products. Goods and services lack diversity and innovation.

Final Thoughts

A few decades back, the market had monopolies of a handful of companies in each sector that controlled the prices and supply of utilities. Now, there is a significant presence of duopolies around the world. It provides just the right amount of competition so that companies can not take market share for granted and still work on products without worrying about disruptions. It is necessary for the sector where quality is more important than price, like airplane manufacturing.

Frequently Asked Questions(FAQs) Q1. How is an oligopoly different from a duopoly?

Answer: In a monopoly, there is just one major supplier. In a duopoly, there are two major suppliers of a particular good or service. In an oligopoly, there are several interdependent firms that influence each other.

Q2. What is a duopoly market? Who introduced the term? Q3. Why is duopoly good?

Answer: Duopoly is a good practice for companies as they can continuously operate the market according to their requirement. They can increase the prices and update the product according to new standards.

Q4. Is duopoly legal?

Answer: With some conditions, a duopoly is legal. Both companies should refrain from collusion, as it may result in higher consumer prices. Collusion may also result in one company becoming a monopoly. Thus, collusion is illegal in the US, but duopoly is legal.

Q5. Is a duopoly form of business beneficial to the economy?

Answer: A duopoly is an efficient form of business. In a sector where quality and constant supply are more important, it is very beneficial as firms can concentrate on the quality of goods without worrying about disruptions.

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Guide For Interview Questions For Sql

This article was published as a part of the Data Science Blogathon.

Introduction on SQL Questions

This blog consists of various topics of SQL and their explanation with answers. There are 12 theoretical questions that are frequently asked in interviews for freshers level and below, there are 15 MCQs related to SQL Questions for practice.

1. What is Database?

A database is a system that helps in storing data, retrieving data, and also helps in manipulating the data. Databases are of various types small, medium, and large. Various Databases are made using the design and modeling approaches which are often complex. A database is usually controlled by a database management system (DBMS).

The most common types of databases are in the form of rows and cols in the form of a table such as excel data. There are various types of databases:

Relational databases






2. What is DBMS?

DBMS stands for Database Management System. The DBMS responsibility is to store, create, update and manage the databases. DBMS ensures that the data is organized in a proper format and there are no loopholes in it and it is easily accessible to developers and also maintains an interface between the databases and end-users of the applications (product).

3. What is RDBMS? How is it Different from DBMS?

                                        RDBMS                                            DBMS

 RDBMS stands for Relational Database Management   System.   DBMS stands for Database Management    System.

 It stores the data in the rows & col in table format.   It stores the data in the format of files.

 It is designed to handle large amounts of data.   It is designed to handle a small amount of data.

 Multiple data elements are accessible together  Individual access to data elements is possible.

 RDBMS support multiple users.  DBMS doesn’t support multiple users.

 A distributed database is supported.  A distributed database is not supported.

 In RDBMS normalization is not achievable.  In DBMS normalization is achievable.

4. What are the Applications of SQL?

The major applications of SQL include:

Writing data integration scripts by the developers and database administrator.

Setting and running analytical queries on the regular basis and making new datasets from the original data.

Retrieving subsets of information within an original database for analytics and visualization purposes

Most common use is Adding, updating, and deleting rows and columns of data in a database

5. Difference between SQL Vs DBMS?

                                SQL                                              DBMS

 SQL stands for Structured Query Language.  DBMS stands for Database Management   System.

It is a query language.  It is a database.

SQL is designed for managing the database  DBMS is designed for providing the security to  database.

It allows the user to create a view of data.  It contains automatic backup and database recovery.

SQL consist of various types of Languages such as DDL, and DML.  It reduced the complexity of the relationship between the data.

For example:. SQL, SQL Server.  For example:, MySQL, Oracle

6. What is Subquery in SQL?

A subquery in SQL is a query in another query. We can also say it as the nested query or an inner query. Mostly subqueries are used to enhance the data to be queried by the main query.

7. What is the SELECT Statement Role in SQL?

The SELECT command is used to display the rows from the database based on the query. The SELECT command is a data manipulation language (DML) command

For example:. We have a student database for a school and we have multiple columns some are StuID, and StuName, and the query is to display the student name.

Query: SELECT * from student;

8. What are the Subsets of SQL?

There are 4 subsets of SQL:

Data definition language (DDL): DDL consists of SQL commands which can be used for defining database schema. DDL deals with the description of the database, update, and delete of the database where it consists of commands like CREATE, ALTER, TRUNCATE, and COMMENT.

Data manipulation language (DML): DML is used to manipulate the existing data in the database. The DML commands are SELECT, UPDATE, INSERT, etc.

Data control language (DCL): DCL controls the access to the data stored in the database and the DCL commands are GRANT and REVOKE.

Transaction Control Language (TCL): TCL is used to deal with the transaction operations in the database. The TCL commands are COMMIT, ROLLBACK, SET TRANSACTION, SAVEPOINT, etc.

9. Explain any 2 Subsets in SQL with their Definition

There are 5 subsets in SQL:

1. Data Definition Language

DDL stands for Data Definition Language where the commands are used to define the database schema. DDL is mostly used to describe the database schema to developers and to create, and modify the overall structure of the database.

The examples of DDL commands are: 

CREATE – Using the create command we can create the database or its objects such as a table, index, function, and views.

DROP – Using the drop command we can delete objects from the database.

ALTER – Using the alter command we can change the structure of the database.

TRUNCATE – Using the truncate command we can remove all the records from a table, including all spaces allocated for the records are removed.

RENAME – Using the rename command we can rename an object which exists in the database.

2. Data Manipulation Language

DML stands for Data Manipulation Language where the commands are used for manipulating the data in the database.

The examples of DML commands are:

SELECT – Using the select command to retrieve data from the database.

INSERT– Using the insert command to insert data into a table.

UPDATE– Using the update command to update existing data within a table.

DELETE– Using the delete command to delete records from a database table.

10. What is JOINT in SQL and Explain any 2 Types?

A JOIN clause is used to combine rows from more than one table based on the same column from both tables.  The two tables are merged and we will retrieve new data from that.

Inner Join: Most of the common types of SQL is Inner Join. Inner Join will return all the rows from multiple tables when the condition is satisfied.

Syntax Inner Join:


Left Join: In Left Join of SQL only rows from the left table are returned and the union of left and right table where the condition is satisfied.

Syntax Left Join:

SELECT * FROM Table_A A LEFT JOIN Table_B B ON chúng tôi = B.col;

Right Join: In Right Join of SQL all the rows from the right table are returned but only the matching rows from the left table where the join condition is fulfilled.

Syntax right Join:

SELECT * FROM Table_A A RIGHT JOIN Table_B B ON chúng tôi = B.col;

Full Join: In Full join of SQL all the records are returned when there is a match in any of the tables. Therefore, it returns all the rows from the left-hand side table and all the rows from the right-hand side table.

Syntax Full Join:

SELECT * FROM Table_A A FULL JOIN Table_B B ON chúng tôi = B.col;

There are a plethora of types of joins, as you can refer to below. Below is a cheat sheet for various types of JOINT in SQL.

11. What is a Primary Key in SQL?

For example, we have student data of a university or college where the columns are roll number and name and we want to display the unique kids having their roll number.  Here, the ROLL Number can be treated as the primary key for a student.

A primary key is a field or the combination of fields that uniquely identify each record in the table. The primary key is a unique key as the table can have only one primary key and it can not be chúng tôi have student data of a university or college where the columns are roll number and name and we want to display the unique kids having their roll number. Here, the ROLL Number can be treated as the primary key for a student.

We can define a primary key in a student table as follows:

CREATE TABLE Student ( roll_number INT PRIMARY KEY, name VARCHAR(45), ); 12.

What is a Foreign Key?

The foreign key is also known as the referencing key. We use a foreign key to link one or more tables together from the database.

A foreign key is often specified as a key that is related to the primary key of another table in simple terms it means that the foreign key field in one table refers to the primary key field of another table. It maintains referential integrity. ACID properties are maintained by the primary key-foreign key relationship. Foreign key also prevents actions that would destroy links between the child and parent tables from the database.

For example, we have student data of a university or college where the columns are roll number and name and we want to display the unique kids having their roll number. Here, the ROLL Number can be treated as the primary key for a student.

We can define a foreign key in a student table as follows:

CREATE TABLE Students (  roll_number INT NOT NULL  name VARCHAR(255)  LibraryID INT  PRIMARY KEY (roll_number)  FOREIGN KEY (Library_ID) REFERENCES Library(LibraryID)  );

Let’s explore some questions for SQL in theoretical and practical. There are 15 questions for SQL in the form of MCQ.

1. Which of the following are some common RDBMS in use?

A. SQLB. Oracle

C. HeidiSQL

D. All of the above

ANSWER: D (All of the above)

2. What is the full form of SQL?

A. Structured Query Language

B. Structured Query List

C. Sample Query Language

D. None of these.

ANSWER: A (Structured Query Language)

3. Which command do we use to create a new table in SQL?





Explanation: CREATE TABLE function is used to create the table in SQL database.

4. Which of the following is not a valid SQL type?






Explanation: DECIMAL is not a valid SQL type because in SQL it is a numeric type.

5. Which of the following commands delete all the rows from the table? 





Explanation: TRUNCATE command is used to delete all the rows without removing the individual rows from the table. TRUNCATE statement is similar to the DELETE statement in SQL just without the WHERE clause in the query.

6. From the option which command is a part of Data Control Language?

A. RevokeB. Grant

C. Both

D. None of this

ANSWER: C (Both)

Explanation: REVOKE and GRANT are the commands for the Data control language.

7. Which of the following SQL functions compares the similarities of 2 strings and returns the result as a 4 character code?





8. Primary key can not be?

A. Depends on the situation

B. Not Null

C. Both Null and Not Null

D. Null


Explanation: A primary key is a field or the combination of fields that uniquely identify each record in the table. The primary key is a unique key as the table can have only one primary key and it can not be null.

9. How Many Primary keys can have in a table?

A. Only 1

B. Only 2

C. Depends on the Columns

D. Depends on the situation

ANSWER: A (Only 1)

Explanation: A primary key is a field or the combination of fields that uniquely identify each record in the table. The primary key is a unique key as the table can have only one primary key and it can not be null.

10. What are Rows of Relation Known as?

A. TupleB. Degree

C. Entity

D. None of this

Explanation: The collection of rows & columns is called the table, whereas a table is known as the relation in the SQL therefore in a relation rows are called the tuples.

11. Which of the following is the full form of DDL?

A. Dynamic data languageB. Data derivation language

C. Data definition language

D. Detailed data language

ANSWER: C(Data definition language)

12. Which of the following are TCL commands?






13. In the command if we are not specifying ASC or DESC after a SQL ORDER BY clause, the result is displayed in which order?





Explanation: In the command, if we are not specifying ASC or DESC after a SQL ORDER BY clause, the result is displayed in which order.

14. Which data manipulation command is used to combine the rows from one or more tables?





15. Which of the following command is not in SQL



D. B and C


Conclusion on SQL Questions

This blog consists of numerous questions related to the topic such as database, SQL, different types of Joint, and many more.  Whenever you are giving your interview always lay your answer in a systemic manner such as giving first the definition and following the explanation with a situation that has an example. Lastly, give the answers with the syntax of the SQL question so the interviewer knows you have an immense and clear knowledge of the given topic.  

Take SQL Questions

I will be laying out some questions (of intermediate level) which are often asked by the interviewer with the answers. In the next series, there will be numerous questions based on coding for SQL.

So stay tuned!

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