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Top 30 SQL Interview Questions and Answers
Almost all SQL job candidates go through the exact same nerve-wracking process. Knowing enough SQL can be very difficult to determine, and more importantly, it prepares you for questions that may be asked in an interview. In fact, there are many different types of SQL database jobs for companies looking for new skills. So if the interview preparation process is difficult or if this is the first step in your preparation, don’t worry.
All planned SQL programming skills are highly desirable and in demand in the market because database management systems (DBMS) are of great value in virtually all software applications. To get the job, applicants must pass an interview where they are asked a series of SQL questions.
We have created a list of SQL interview questions and answers that are likely to be considered during an interview session. Additionally, candidates tend to be asked questions that range from basic SQL to advanced SQL, depending on their knowledge and several other determining factors. This article covers SQL Interview Questions,SQL Interview Questions and Answers in 2022,SQL Interview Questions and Answers,SQL Interview Questions for Freshers,SQL Interview Questions for Experienced.
SQL Interview Questions and Answers
Q1. What is SQL?
Structured Query Language or SQL, used to interact with databases. It is a traditional language used to perform responsibilities such as updating, retrieving, deleting, and inserting data from databases.
Q2. What is a database table?
A table is a database object used to store records in an array of rows and columns containing data.
Q3. What is the difference between SQL and MySQL?
SQL is the traditional language for retrieving and building structured databases. In contrast, MySQL is a relational database management operator such as Oracle, SQL Server, and IBM DB2 used to manage SQL databases.
Q4. What does join mean in SQL?
The JOIN clause is used to combine rows from two or more tables based on related columns.
Q5. How many types of joins are there?
There are four types of joins.
Inner Joins: SQL inner joins are a common type of join. Applied to return all rows from different tables with join conditions satisfied.
Right Join: A SQL Right Join is used to return all rows from the right table, but only matching rows from the left table where the join condition is satisfied.
Left Join: A Left Join in SQL is practiced to return all rows from the left table, but only matching rows from the right table where the join condition is satisfied.
Full Join: A full join returns all records if there is a match in any table. So all rows from the left table and all rows from the right table are restored.
Q6. What kind of SQL commands?
SQL commands are classified into the following types:
DML – Data Manipulation Language
DQL – Data Query Language
TCL – Transaction Control Language
DDL – Data Definition Language
DCL – Data Control Language
Q7. What TCP/IP port did SQL Server originally use?
By default, SQL Server runs on TCP port number 1433.
Q7. Are null values the same as zeros or spaces?
No, null values are equal or not equal to zeros or spaces. A null value represents a value that cannot be used, explained, assigned, or applied. Zero is a number, space is a number.
Q8. What are the different DCL commands in SQL?
DCL commands are implemented to create roles, grant privileges, and control access to database objects.
GRANT: Implement user access.
DENY: Deny user permission.
REVOKE: To remove user access
Q9. What is meant by database?
A database is a coordinated combination of data stored and retrieved in digital form from local or remote computer systems. Additionally, databases can be large and complex, and such databases are created using fixed design and modeling procedures.
Q10. Define a data warehouse?
Data warehouses connect to a central repository of data from a variety of sources. This data is combined, modified and prepared for mining and online processing.
Q11. What is a DBMS?
(DBMS) A database management system is a scheme that controls the creation, maintenance, and performance of databases. A DBMS is also known as a file manager that works with databases rather than storing data in a file system.
Q12. What are the two types of DBMS?
There are two types of DBMS:
Relational Database Management Systems: Data is collected in relations (tables). For example, MySQL.
Non-Relational Database Management System: No theory about relationships, tuples, and attributes. Example – MongoDB.
Q13. How is the DISTINCT statement used? And what is it good for?
DISTINCT is used in SELECT statement. If your records contain duplicate values, use the DISTINCT statement to select distinct values among the duplicate records.
SELECT DISTINCT column_name(s)
Q14. What are tables and fields?
A table is a collection of data arranged in a model of rows and columns. Columns can be sorted vertically and rows can be sorted horizontally. Additionally, a table has a certain number of columns called fields, but can have any number of rows called records.
Q15. What does primary key mean?
A primary key is a combination of fields that uniquely defines a row. It is a unique key of a certain type and has an implicit NOT NULL constraint. Indicates that the primary key value cannot be null.
Top 30 SQL Interview Questions and Answers 2022
Q16. Name the different types of index configurations possible for SQL tables?
In SQL, a table can have the following index organization:
- A clustered index
- No indexes
- A non-clustered index
- A clustered index and many non-clustered indexes
- Many non-clustered indexes
Q17. Describe the transaction?
A transaction can be described as a series of tasks that are logically performed on the database to produce an accurate result. Operations such as updating, creating, and deleting records in the database come from transactions. Simply put, a transaction represents a group of SQL queries that are executed against database records.
Q18. What is query optimization?
The phase of finding the plan for an evaluation query with the lowest estimated cost is called query optimization.
Q19. What does trigger mean?
A trigger in SQL is a type of stored method used to create a response to a specific action performed on a table. B. INSERT, UPDATE, or DELETE. You can explicitly request a trigger on a table in your database. Also, actions and events are the two main elements of SQL triggers. When a particular action is implemented, events are raised in response to that action.
Q20. Define a view?
A view is a virtual table consisting of a subset of data constrained to a table. Views are virtually non-existent and require less storage space. Views can include data from one or more additional tables that are integrated.
Q21. Define the stored procedure?
A stored procedure is a function containing many SQL statements to retrieve the database system. Many SQL statements are embedded in stored procedures and executed wherever and whenever needed.
Q22. Describe the difference between the DELETE and TRUNCATE commands.
DELETE: You can use the DELETE command to delete rows from a table and use the WHERE clause for conditional collection of parameters. Commits and rollbacks can be delivered after removing statements.
TRUNCATE removes all rows from a table. Cannot return truncate operation
Q23. Describe the difference between the DROP and TRUNCATE commands?
While the TRUNCATE command is extracting all rows from the table, the DROP command drops the table and cannot be removed from the database.
Q24. Declare a self-join?
A self-join is a regular join that joins a table to itself based on the relationships between the columns of the table itself. A self-join implements an INNER JOIN or LEFT JOIN clause, and a table alias is used to specify a different name for the table in the query.
Q25. Define a recovery model?
The recovery model basically tells SQL Server what data to store in the exchange log and how much.
Q26. What are the transaction controls?
There are four transaction controls.
Commit: It is a practice to save all adjustments made during a transaction.
ROLLBACK: Used to rollback a transaction. All changes made by the transaction are returned, leaving the database as before.
SET TRANSACTION: Insert the name of the transaction.
SAVEPOINT: It is a practice to specify a point to push back a transaction.
Q27. What are the famous Database Management Systems in the IT Industry?
MySQL, Oracle, PostgreSQL, Microsoft SQL Server, DB2, Sybase, MongoDB, Microsoft Access, etc.
Q28. What are the different subsets of SQL?
Data Definition Language (DDL) – Allows you to perform various operations on the database such as ALTER, CREATE and DELETE objects.
Data manipulation language (DML) allows you to access and manipulate data. It also assists in update, insert, delete, and restore data from databases.
Data Control Language (DCL) – Allows you to control access to databases. For example, grant and revoke permissions.
Q29. What is meant by data integrity?
Data integrity describes the accuracy and flexibility of the data collected in the database. It also represents integrity constraints for setting business rules for data when accessed by an application or database.
Q30. What are the benefits of query optimization?
- Output is produced faster.
- Manage more queries in less time.
- Reduce time and domain complexity
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Above we’ve covered the most important SQL Interview Questions and Answers in 2022,SQL Interview Questions for Freshers,SQL Interview Questions for Experienced, perfect for both new students and professionals. Becoming a your technical skills and knowledge, but also helps secure your career. That said, this role is important for any type of her IT organization where she can learn and progress to more advanced levels. So take on the role of software developer. Use the questions above to prepare for your interview and share your experiences and doubts in the comments section.