Interview Questions Answers in SQL PLSQL, STL, C

Explain the concept of normalization.

Answer

Normalization is the process of organizing data to minimize redundancy and improve data integrity.
Normal Forms:
• 1NF: Eliminate repeating groups, ensure atomicity.
• 2NF: Ensure 1NF and remove partial dependencies.
• 3NF: Ensure 2NF and remove transitive dependencies.
• BCNF: Ensure every determinant is a candidate key.

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Question { 1378 }

What is a CTE (Common Table Expression), and how is it different from a subquery?

Answer

• CTE: Temporary result set defined using WITH and reusable within the query. Improves readability for complex queries.
• Subquery: Nested query executed each time it is called. Example:
WITH SalesCTE AS (
SELECT employee_id, SUM(sales) AS total_sales
FROM sales
GROUP BY employee_id
)
SELECT * FROM SalesCTE WHERE total_sales > 5000;

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Question { 1535 }

What are triggers, and when would you use them?

Answer

A trigger is a block of PL/SQL code automatically executed in response to certain events (e.g., INSERT, UPDATE, DELETE) on a table.
Example Trigger:
CREATE OR REPLACE TRIGGER EmployeeAudit
AFTER INSERT ON employees
FOR EACH ROW
BEGIN
INSERT INTO audit_log(employee_id, action, action_date)
VALUES (:NEW.id, 'INSERT', SYSDATE);
END;

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Question { 1558 }

Explain References in C++

Answer

In this set of fresher-level C++ interview questions, one frequently encountered question is about references. Declaring a variable as a reference provides an alternate name for an existing variable.
A reference variable is created by placing an ‘&’ in the declaration. Essentially, a reference acts as an alias for another variable, allowing access to the associated variable through either its original name or the reference itself.
Syntax:Using references facilitates easier manipulation of variables without copying their values, making them particularly useful in function parameters and return types.

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Question { 1441 }

What Is Operator Overloading in C++?

Answer

In C++ interview questions, one frequently asked question is about operator overloading. Operator overloading is a form of compile-time polymorphism that allows operators to be given special meanings for user-defined data types.
This feature enables most operators to be redefined or overloaded to perform operations on these user-defined types. For instance,
C++ allows the addition of variables of user-defined data types in a manner similar to built-in data types.

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Question { 1066 }

Compare SQL and PL/SQL.

Answer

SQL is a domain-specific language to manage and manipulate relational databases. It primarily deals with querying, inserting, updating, and deleting data in a database. On the other hand, PL/SQL is a procedural language that extends SQL by adding programming constructs like variables, loops, and exception handling. PL/SQL is used for writing stored procedures, functions, and triggers, allowing for more complex and reusable database logic.

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Question { 1916 }

Do you know the basic structure of PL/SQL?

Answer

Yes, the basic structure of a PL/SQL block includes:
• Declaration section: Where you define variables, constants, and cursors.
• Execution section: Where you write the actual PL/SQL code, including SQL statements and procedural logic.
• Exception handling section: Where you handle errors and exceptions that may occur during execution.

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Question { 1826 }

What Is a Trigger? How Do You Use It?

Answer

A Triger is a database object in PL/SQL that automatically executes actions in response to specific events, such as insertions, updates, or data deletions in a table. Triggers are typically used to enforce business rules, maintain data integrity, and automate tasks. You create and define triggers using PL/SQL code and attach them to database tables.

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Question { 1552 }

What data types does pl/SQL have?

Answer

PL/SQL supports various data types, including:
• Scalar data types like VARCHAR2, NUMBER, DATE, and BOOLEAN.
• Composite data types like RECORD and TABLE.
• Reference data types like REF CURSOR and PL/SQL TABLE.

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Question { 1662 }

Explain the PL/SQL compilation process.

Answer

The PL/SQL compilation process involves:
• Parsing: The PL/SQL code is checked for syntax errors.
• Compilation: The code is converted into a format the Oracle Database can execute.
• Storage: The compiled code is stored in the database.
• Execution: When the PL/SQL code is called, it is executed by the database engine.

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Question { 1456 }

Tell me what a package consists of.

Answer

A PL/SQL package contains related procedures, functions, variables, and other PL/SQL constructs. It consists of two main parts:
• Package Specification: This defines the public interface of the package, including procedures, functions, and global variables that other programs can access.
• Package Body: This contains the actual implementation of the functions and procedures defined in the specification.

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Question { 1680 }

What are the benefits of using PL/SQL packages?

Answer

Using PL/SQL packages offers several benefits, including:
• Encapsulation: You can encapsulate related code and data within a package, promoting modular and organized code.
• Reusability: Packages allow you to reuse code across multiple programs and reduce redundancy.
• Information Hiding: You can hide implementation details by exposing only the necessary interfaces in the package specification.
• Improved Performance: Packages are precompiled and stored in the database, which can enhance performance.

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Question { 1313 }

Do you understand the meaning of exception handling?

Answer

Yes, exception handling in PL/SQL is the process of handling errors or exceptional conditions that may occur during program execution. It allows you to gracefully handle errors by specifying actions to take when a particular exception occurs, such as logging the error, rolling back transactions, or raising custom exceptions.

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Question { 2385 }

Give me some examples of predefined exceptions.

Answer

Predefined exceptions in PL/SQL include:
• NO_DATA_FOUND: Raised when a SELECT statement returns no rows.
• TOO_MANY_ROWS: Raised when a SELECT INTO statement retrieves multiple rows.
• DUP_VAL_ON_INDEX: Raised when attempting to insert a duplicate value into a specific index.
• ZERO_DIVIDE: Raised when dividing by zero.

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Question { 1318 }

What is a Deque?

Answer

A double-ended queue is called a deque.
You can add or remove components from either end of this structure.

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