Most asked SQL Interview Questions for Freshers
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Most asked SQL Interview Questions for Freshers : Structured Query Language (SQL) is a cornerstone skill for any aspiring data professional or software developer. Whether you’re aiming for a role in database management, data analysis, or software engineering, proficiency in SQL is a must.

1. What is SQL?

SQL, or Structured Query Language, is a standard programming language used for managing and manipulating relational databases. It enables users to perform tasks such as querying data, updating records, and managing database structures.

2. Name the different types of SQL commands.

SQL commands are broadly categorized into four types:

  • Data Definition Language (DDL): Used for defining and managing database objects.
  • Data Manipulation Language (DML): Used for manipulating data within tables.
  • Data Control Language (DCL): Used for managing access permissions and privileges.
  • Transaction Control Language (TCL): Used for managing transactions.

3. Explain the difference between SQL and MySQL.

SQL is a standardized programming language used for managing relational databases, while MySQL is an open-source relational database management system (RDBMS) that implements SQL.

4. What is a primary key in SQL?

A primary key is a column or set of columns that uniquely identifies each row in a table. It ensures data integrity by preventing duplicate and null values.

5. How do you add a new record to a table in SQL?

You can add a new record using the INSERT INTO statement:

INSERT INTO table_name (column1, column2, …)
VALUES (value1, value2, …);

6. What is the purpose of the SQL “SELECT” statement?

The SELECT statement is used to retrieve data from one or more tables in a database. It allows you to specify which columns to retrieve and apply filtering and sorting criteria.

7. Explain the difference between the WHERE and HAVING clauses in SQL.

The WHERE clause is used to filter rows before grouping in aggregate functions, while the HAVING clause is used to filter groups after grouping.

8. What is a foreign key in SQL?

A foreign key is a column or set of columns that establishes a relationship between two tables. It ensures referential integrity by enforcing a link between the child and parent tables.

9. How do you update data in a table using SQL?

You can update data using the UPDATE statement:

UPDATE table_name
SET column1 = value1, column2 = value2, …
WHERE condition;

10. Explain the purpose of the SQL “GROUP BY" clause.

The GROUP BY clause is used to group rows that have the same values into summary rows. It is often used with aggregate functions to perform calculations on groups of rows.

11. What is a SQL view?

A SQL view is a virtual table generated by a query. It allows users to access and manipulate data as if it were a regular table, without storing the data itself.

12. How do you delete data from a table using SQL?

You can delete data using the DELETE FROM statement: DELETE FROM table_name WHERE condition;

13. Explain the purpose of the SQL “DISTINCT” keyword.

The DISTINCT keyword is used to retrieve unique records from a query result set, eliminating duplicate rows.

14. What is a SQL stored procedure?

A stored procedure is a set of SQL statements stored in the database catalog. It can be invoked by users or applications to perform specific tasks or operations.

15. How do you retrieve data from multiple tables using SQL?

You can retrieve data using JOIN operations:

SELECT columns FROM table1 INNER JOIN table2 ON table1.column = table2.column;

16. Explain the purpose of the SQL “LIKE” operator.

The LIKE operator is used to search for a specified pattern in a column. It allows the use of wildcard characters (% and _) to represent zero or more characters.

17. What is a SQL trigger?

A trigger is a stored procedure that automatically executes in response to certain events, such as insertions, updates, or deletions, on a table.

18. How do you perform aggregate functions in SQL?

Aggregate functions are used to perform calculations on a set of values. Examples include SUM, AVG, COUNT, MIN, and MAX.

19. Explain the purpose of the SQL “ORDER BY" clause.

The ORDER BY clause is used to sort the result set returned by a query based on one or more columns.

20. What is a SQL transaction?

A transaction is a sequence of SQL operations that are treated as a single unit of work. Transactions ensure data integrity by allowing changes to be either committed or rolled back as a whole.

21. How do you create a new table in SQL?

You can create a table using the CREATE TABLE statement: CREATE TABLE table_name ( column1 datatype, column2 datatype, ... );

22. Explain the purpose of the SQL “UNION" operator.

The UNION operator is used to combine the results of two or more SELECT statements into a single result set. It eliminates duplicate rows by default.

23. What is a SQL index?

An index is a database object used to improve the speed of data retrieval operations on a table. It consists of one or more columns from the table and a pointer to the location of the data in the table.

24. How do you drop a table in SQL?

You can drop a table using the DROP TABLE statement:

DROP TABLE table_name;

25. Explain the purpose of the SQL IN operator.

The IN operator is used to specify multiple values in a WHERE clause. It allows you to filter rows based on a set of predefined values.

26. What is a SQL constraint?

A constraint is a rule defined on a table column to enforce data integrity. Common constraints include PRIMARY KEY, FOREIGN KEY, NOT NULL, and UNIQUE.

27. How do you add a new column to an existing table in SQL?

You can add a new column using the ALTER TABLE statement: ALTER TABLE table_name ADD column_name datatype;

28. Explain the purpose of the SQL NULL value.

The NULL value represents missing or unknown data in a column. It is not equivalent to zero or an empty string and requires special handling in SQL queries.

29. What is a SQL join?

A join is a SQL operation used to combine rows from two or more tables based on a related column between them.

30. How do you create an index in SQL?

You can create an index using the CREATE INDEX statement:

CREATE INDEX index_name ON table_name (column1, column2, ...);

31. Explain the purpose of the SQL GROUP BY clause.

The GROUP BY clause is used to group rows that have the same values into summary rows. It is often used with aggregate functions to perform calculations on groups of rows.

32. What is a SQL view?

A SQL view is a virtual table generated by a query. It allows users to access and manipulate data as if it were a regular table, without storing the data itself.

33. How do you delete data from a table using SQL?

You can delete data using the DELETE FROM statement: DELETE FROM table_name WHERE condition;

34. Explain the purpose of the SQL DISTINCT keyword.

The DISTINCT keyword is used to retrieve unique records from a query result set, eliminating duplicate rows.

35. What is a SQL stored procedure?

A stored procedure is a set of SQL statements stored in the database catalog. It can be invoked by users or applications to perform specific tasks or operations.

36. How do you retrieve data from multiple tables using SQL?

You can retrieve data using JOIN operations: SELECT columns FROM table1 INNER JOIN table2 ON table1.column = table2.column;

37. Explain the purpose of the SQL LIKE operator.

The LIKE operator is used to search for a specified pattern in a column. It allows the use of wildcard characters (% and _) to represent zero or more characters.

38. What is a SQL trigger?

A trigger is a stored procedure that automatically executes in response to certain events, such as insertions, updates, or deletions, on a table.

39. How do you perform aggregate functions in SQL?

Aggregate functions are used to perform calculations on a set of values. Examples include SUM, AVG, COUNT, MIN, and MAX.

40. Explain the purpose of the SQL ORDER BY clause.

The ORDER BY clause is used to sort the result set returned by a query based on one or more columns.