Top 25 SQL Interview Questions and Answers in 2022


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Preparing for an interview gives you the courage to appear before the interviewing panel. This article provides you with the top 25 SQL interview questions along with the best way to approach each of them. Refer to them for quick preparation of major SQL concepts before you can appear for your interview.

1. Why Are You Interested In This Role.

I have recently graduated with a master’s degree in database administration. Previously I attained a bachelor’s degree in computer science. I have also had a one-year internship in a software development company. During this time, I gained a lot of experience in maintaining adherence to a data management policy, ensuring that organization databases are functional, backing up data in case of memory loss, etc.

Since when I graduated with my master’s degree, I have been on the lookout for a job opening that I can be happy doing. After going through your job posting for this job, I found that this is a job that I would love to do. Moreover, I certify the requirements for this role.

2. Describe Your Experience Relating To The Role You Are Seeking

I have been doing a similar role for close to five years now.  I have been the first respondent to database issues that would arise including performing periodic troubleshooting and maintenance. I would ensure that the database is backed up such that it can be recovered in case of any memory loss.I can effectively report on metrics about usage and performance. I would also suggest changes and improvements for database protection and maintenance. Besides, I have developed excellent problem-solving, communication, administrative, technical, and interpersonal skills.  I strongly believe that my experience and extensive knowledge of database administration will help me succeed in this role.

3. What Roles Do You Expect To Be Performing Should You Get This Job?

I had gone through the job posting for this role before applying for it. I understand that I will be doing the following duties:

Why Should We Hire You? 5 Best Answ...
Why Should We Hire You? 5 Best Answers
  • Designing and implementing a database depending on the preferences of the end-users
  • Building quality database systems based on the end-users preferences
  • Distributing data to the right users
  • Recovering and backing up data
  • Providing proactive and reactive data management  support
  • Performing tests and evaluations to ensure data privacy, security, and integrity
  • Regularly collaborating with database programmers and IT project managers

4. What Qualities Do You Have To Enable You To Perform Your Roles

I am familiar with database queries and database management best practices. I know database theories and design, database management best practices, database structure languages, IT security best practices,  etc. Besides, I have strong problem-solving, critical thinking, multitasking, customer service, and communication skills. I can explain complex ideas in layman’s language and I am attentive to details.

5. Why Do You Think That You Are The Best Fit For This Role?

I have a bachelor’s degree in computer science. I also have a NET certification.  I’m proficient in data manipulation languages such as oracle database, PostgreSQL, MS SQL, and Hadoop. Previously, I worked as a data administrator for four years. During this time, I gained a lot of experience in maintaining adherence to a data management policy, ensuring that organization databases are functional, backing up data in case of memory loss, etc. Besides, I am highly organized, and responsible, and I can work under pressure.  Additionally, I have strong problem-solving, communication, analytical mindset, and administration skills. Should you allow me to work in this company, I will use my experience, skills, education, and strong qualities to exceed your expectation for this role.

6. Discuss The Features Of SQL

  • SQL provides multiple commands such as DDL which gives commands that define relation schemas, modify relational schemas, and delete relations.
  • Contain data manipulation language used for manipulating data in a table.
  • SQL is used for a relational database which makes it easy to learn and use
  • It has a high performance making it easy to retrieve data
  • Has a vertically scalable database. This means that a user can increase the load on a single server by adding more CPUs, SSDs, or RAM.
  • SQL Server contains multiple security enabling features such as encrypted communication over TLS/SSL, and Windows Data Protection API (DPAPI) to encrypt data at rest, authentication, and authorization.
  • It is portable across different computer systems

7. State Some Commands In Data Definition Language (DDL)That You Are Familiar With

DDL provides commands that define deleting relations, and relation schemas, as well as modifying relational schemas. These commands include:

  • Create command: You use this command when you want to create a new table
  • Drop command: This command is used when a programmer wants to delete a table
  • Alter: The command is used when a user wants to modify the structure of a table
  • Rename: This command is used when a programmer changes a table’s name.
  • Truncate: This is a command used when a user wants to delete all data in a table without altering the structure of the table

8. Name The Four Commands In Data Manipulation Language (DML)

  • Select command: This is a command used by a user to query information from a table. This means that the command help to select a set of data from a table.
  • Insert command: This is a command used by a user to add new rows or records to a table
  • Update command: You use this command when you need to change data in a

table.

  • Delete command: This is a command a user uses to delete data or other records in a table.

9.  Highlight The Advantages Of Using SQL

There are several advantages of using SQL including:

  • No coding is needed- it does not need substantial code knowledge to manage the database system. Thus, making it easy to manage a database.
  • High speed- It provides queries that help a user efficiently and quickly retrieve a large amount of data from a database.
  • Well-defined standards- SQL is compatible with many standards such as ANSI and ISO.
  • Interactive language-It can be used to communicate with the database as well as receive solutions to difficult questions in seconds.
  • Portability- it can work well with some mobile phones, servers, PCs, and laptops.
  • Multiple data view- With the help of SQL, it is easy to make different views of the database structure.

10. Briefly Explain The Structure Of An SQL Query?

There are three clauses that make up a typical SQL query. These are Where, From, and Select. The select clause contains what is expected in the final result while the relations that one needs to access in order to get the result goes in the from clause. Then, the where clause specifies how the relation should be operated so as to get the desired results.

11. Describe The Select Clause In SQL

The SELECT clause may be expressed in its basic form as a list of the fields you wish to extract from the database, separated by commas. The table that is provided in the FROM clause must have the fields that one specifies in this clause.

In the resulting query, the majority of the fields that are retrieved are shown as columns.  But certain database fields have a specific purpose and are hence not visible like columns within the resulting query. To get the required functionality and query results one needs, it is important to be aware of the “special” attributes that should be included in a list separated by commas.

12. What General Rules Should You Observe When Constructing Object Names In SQL?

Within the object name’s scope, object names should be distinctive. In a database system, there are several rules:

  • The names of any two databases cannot be the same.
  • A user cannot have the same name as an existing database since creating a user automatically generates a database name similar to a user’s name.
  • Each profile must have a unique name.
  • Two roles cannot have the same name.
  • Roles and Profiles can share names, but neither Roles nor Profiles can share names with databases.

Then, within a named database, triggers, user-defined functions, hash or join indexes, stored procedures, tables, views, and macros should all have distinctive names.

13. What Is NULL Statement In SQL?

The statement NULL is an executable command that has no effect. When an executable statement is needed but no SQL execution is desired, such as within the IF-THEN-ELSE statement, the NULL statement can serve as a placeholder.

14. What Is an SQL UPDATE Statement?

This is simply a statement whose purpose is to alter the data in one or multiple records in a table. A subset of the rows may be selected using a condition, or all the rows may be updated. The modified value must not violate any of the applicable restrictions and the user must have the right to modify data on the table or column, that is, UPDATE privilege.

15.  Why Is Continuous Integration Important During Software Development?

Continuous integration specifically needs code integration into repositories that are shared many times every day in a project. Continuous integration is important because it verifies each code integration that comes about during the early detection of runtime bugs, errors, and other potential problems in development.

16. What Are SQL Constraints?

Constraints are rules and restrictions in SQL that are applied to a table or column to prevent unwanted data from being inserted into the table or column. This enhances the reliability and accuracy of data in the database. A programmer can create constraints on one or many columns of any table. Constraints maintain the accuracy and integrity of the data in the table.

17. Highlight Constraints That Are Commonly Used In SQL

SQL Server has the following types of constraints’:

  • Not Null Constraint-  this type of constraint restricts null values from being inserted into a column.
  • Check Constraint- This constraint check for a particular condition before a data get inserted into a table
  • Default constraint- This is a constraint that allows a default value to be inserted into a column when a value is not specified
  • Unique constraint- it makes sure that every row for each column has a unique value
  • Primary Constraint- This constraint identifies every row in a table. It can’t accept duplicate and null data.
  • Foreign Constraint-  This is a constraint that creates a relation between two tables

18. What Are ACID Properties In A Transaction?

To obtain consistency in a database before inserting any value, some properties are followed. These properties are known as ACID properties.

They are:

Atomicity-This property  states that the transaction must take place in full and can’tbe left in the middle

Consistency- This property maintains data integrity to ensure that valid data are inserted into the database.

Isolation- This property controls concurrency

Durability – the property ensures that a transaction remains committed

19. What Does Normalization Mean In SQL?

The term “normalization” refers to the process of removing data redundancy and improving data integrity in a table. Normalization also aids in the database’s organization. It’s a multi-step procedure for converting data into a tabular format and removing duplicate data from relational tables. Normalization is the process of organizing a database’s columns and tables such that database integrity constraints may correctly execute their dependencies. It is a method of deconstructing tables in order to remove data redundancy as well as undesired features such as Insertion, Update, and Deletion anomalies.

20. Explain What You Understand By SQL Injection

SQL Injection refers to a code-based vulnerability, which allows attackers to read as well as access sensitive database data. Attackers can use SQL queries to edit, add, update, or remove records in a database, bypassing application security protections. A successful SQL injection attack against a website or online application that uses relational databases like MySQL, Oracle, or SQL Server can be disastrous. Many security breaches have occurred in recent years as a result of SQL injection attacks.

21. Describe Two Types Of SQL Injection

The first is Union-based SQL injection. In this case, the UNION SQL operator is often used to combine the results of two or more database select queries to form a single HTTP response. You may write your queries directly in the URL or combine numerous statements in the input fields to see if you can get a response.

The second SQL injection is an Error-based SQL injection. Here, the attacker conducts operations that cause the database to create error messages. You can figure out what database it uses, what server version the handlers are on, and so on by looking at the error message.

22. Explains Some Ways To Prevent SQL Injections

Using parameterized queries and prepared statements is one of the great ways to prevent injections. Parameterized statements guarantee that the arguments given into SQL statements are handled securely.

Object-relational mapping is another prevention strategy. To transfer SQL result sets into code objects more smoothly, most development teams choose to utilize Object Relational Mapping frameworks.

Escaping inputs is another great approach to guard against many SQL injection threats. Many languages provide built-in functions for achieving this. When employing escape characters within a code, you need to know where the SQL statement is constructed.

23. Tell Us Some Differences Between SQL And My SQL

SQL constitutes a query programming language for managing relational databases. MySQL is a SQL-based relational database management system. SQL is a querying and operating language for database systems. MySQL allows you to manage, save, edit, and remove data in a structured manner. There are no connectors supported in SQL. MySQL includes a built-in tool called MySQL Workbench that helps you create, design, and develop databases. SQL has a basic standard format that does not require numerous or frequent modifications. MySQL comes in a variety of flavors and is updated often. Lastly, only one storage engine is supported by SQL while MySQL is more versatile since it supports different storage engines and plug-in storage.

24. How Are RDBMS And DBMS Different?

A database management system (DBMS) is software that allows you to create, save, manage, update, and retrieve data from databases. On the other hand, a relational database management system (RDBMS) refers to software that enables the development and management of databases for efficient data retrieval, updating, and storage. In a DBMS, data is stored in files. It can be structured in a hierarchical or navigable format. In RDBMS, tables are used to store data. There is no hierarchy; instead, a relational model is used. Only a single user is supported by the Database Management System but multiple users can access databases using a Relational Database Management System.

25. Define A Join In SQL And List Some Types

A join is a keyword that is used to query data from several tables depending on the association between fields within a table. Some of the types of joins are inner join, right join, full join, and left join.

Conclusion

These SQL interview questions and answers cover areas that are commonly tested by many interviewers. So, by studying and practicing them, you will certainly increase your chances of getting hired. Good luck!

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