Most Common SQL Questions & Answers You Must Know For Your Next Interview

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sql vs nosql

Here, SQL also is known as ‘Structured Query Language’ is a computer language that fetches as well as manage information stored in any database.
Hence, Programmers well versed in this language are offered fruitful jobs.
And the competition to secure these jobs is quite raging.

Therefore, whether you are a fresher or an experienced professional, here are a few essential questions you should go through in order to succeed in your next interview.

1. What is SQL?

Furthermore, SQL is a computer programming language that you can use in order to retrieve, update, manipulate, manage as well as store the information you have stored on a database.

2. What are the subsets of SQL?

Here, There are three types of subsets of SQL:

  • A Data Definition Language- including operations like CREATE, ALTER, DELETE.
  • Data Manipulation Language- offers access as well as manipulation.
  • Data Control Language- offers access control of the data.

3. What is DBMS?

Here, DBMS also is known as the Database Management System, is a software that offers interaction between you as well as the database in order to collect as well as analyze data.

4. What are the different types of DBMS?

There are two types of DBMS:
Relational Database Management System
Non-Relational Database Management System

5. What do you understand by tables as well as rows in SQL?

In addition to, a relational database system contains one or more objects called tables.
Hence, The data or information for the database is stored in these tables. Tables are uniquely identified by their names as well as are comprised of columns as well as rows. Columns contain the column name, data type, as well as any other attributes for the column.

6. What do you understand by a JOIN Clause?

Here, You can use the JOIN clause to merge data when the data in the rows of a table are related by one or more common table.
JOIN Clause is of four types:

  • inner,
  • right,
  • left as well as,
  • full

7. What do you mean by DISTINCT Statement as well as how is it used?

Hence, in case your records containing duplicate values, The DISTINCT statement is a SELECT command you can use to choose specific values among those duplicates.

8. List all the clauses which are used in SQL?

Clauses are commands in the SQL software.
There are 6 main types of clauses:

  • JOIN

9. What do you mean by CONSTRAINTS? What are its types?

Here, These are commands you can use to set the rules for your data. Any operations violating the set rules are aborted by the constraints.
There are five types of constraints:

  • NOT NULL- columns cannot be left empty or null
  • UNIQUE – ensures values in cells are unique as well as not repeated
  • PRIMARY KEY – to identify a record
  • FOREIGN KEY – ensures the integrity of data
  • CHECK – makes certain values in cells meet the set rules.

10. What are Scalar Functions?

You can use the Scalar Function to return a single value for the input value.
They are:

  • UCASE ()
  • LCASE ()
  • MID ()
  • FORMAT ()
  • LEN ()
  • ROUND ()

11. What is view as well as how can it be updated?

It is a simulated table containing your information from the fields of one or more different tables. 
To update the view the commands you can use CREATE as well as REPLACE.

12. What is Injection?

You can use this technique to access sensitive data where a malicious command is entered into an entry field in order to open a certain database to the attacker.

13. What is Subquery?

A query whose output serves as input for another query is called a subquery.

14. What is the difference between SQL as well as MYSQL?


SQL is involved in the creation as well as accessing your databases, whereas MySQL is a Relational DBMS which uses SQL as the standard language.

15. What is data integrity?

The authenticity as well as consistency of data in your database is called its integrity.

16. What are clustered as well as a non-clustered index?

They are performance tuning methods.
The clustered index offers easy as well as quick retrieval as well as it alters the way your data is stored in rows as well as columns, sorting it out.
A non-clustered index is comparatively slower to use as well as it does not affect your data storage.

17. What are DE normalization as well as Normalization?

DE normalization is a technique you can use to better the performance through the introduction of redundancy into a table.
Normalization is data organization techniques that help avoid any duplication as well as redundancy.

18. What is ACID property? 

It stands for Atomicity, Consistency, Isolation, as well as Durability.
It ensures the reliability of your data transactions.

19. What is a Trigger?

It is a procedure that automatically executes in wake of data modifications.

20. What are the operators?

They are commands in the language. 
They are:

  • Arithmetic
  • Comparison
  • Logical

21. What is DROP, DELETE as well as TRUNCATE?

They are commands you can use to modify your data.

  • DROP irreversibly removes the entire table from your database.
  • DELETE removes a single row from your table.
  • TRUNCATE removes all rows from your table.

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