These questions cover various fundamental concepts in databases and SQL that are essential for freshers
Q-1. What is a database?
A database is a structured collection of data that is organized and stored in a computer system. It allows for easy retrieval, manipulation, and management of data.
Q-2 What is DBMS?
DBMS stands for Database Management System. It is software that enables users to define, create, maintain, and control access to databases.
Q-3 What are the types of DBMS?
There are mainly four types of DBMS: hierarchical, network, relational, and object-oriented DBMS.
Q-4 What is SQL?
SQL (Structured Query Language) is a standard language for accessing and manipulating databases. It is used to perform tasks such as querying data, updating data, and defining database schema.
Q-5 What is a table in a database?
A table is a collection of related data organized in rows and columns. It is the basic unit of storage in a relational database.
Q-6 What is a primary key?
A primary key is a unique identifier for each record in a table. It ensures that each row in a table is uniquely identifiable and helps enforce entity integrity.
Q-7 What is a foreign key?
A foreign key is a field in a table that refers to the primary key of another table. It establishes a link between two tables and enforces referential integrity.
Q-8 What is normalization?
Normalization is the process of organizing data in a database to reduce redundancy and dependency. It involves breaking down large tables into smaller ones and defining relationships between them.
Q-9 What is denormalization?
Denormalization is the process of intentionally adding redundancy to a database for performance reasons. It involves combining tables and duplicating data to eliminate the need for joins and improve query performance.
Q-10 What is a transaction?
A transaction is a sequence of operations performed on a database that must be executed as a single unit. It follows the ACID properties (Atomicity, Consistency, Isolation, Durability) to ensure data integrity.
Q-11 What is ACID properties?
ACID stands for Atomicity, Consistency, Isolation, and Durability. These are the four properties that ensure the reliability of transactions in a database system.
Q-12 What is a view?
A view is a virtual table derived from one or more tables in a database. It presents a subset of data from the underlying tables and can be used to simplify complex queries or provide security restrictions.
Q-13 What is indexing?
Indexing is the process of creating an ordered data structure (index) on a database table to improve the speed of data retrieval operations. It allows for faster searching, sorting, and filtering of data.
Q-14 What is a stored procedure?
A stored procedure is a precompiled set of SQL statements that are stored in the database and can be executed by invoking the procedure's name. It helps improve performance, maintainability, and security of database applications.
Q-15 What is a trigger?
A trigger is a special type of stored procedure that is automatically executed in response to certain events (e.g., insert, update, delete) occurring in a database table. Triggers are used to enforce business rules, maintain data integrity, and automate tasks.
Q-16 What is a database schema?
A database schema is a blueprint that defines the structure of a database, including tables, columns, data types, relationships, constraints, and indexes.
Q-17 What is a constraint?
A constraint is a rule enforced on the data in a database to maintain data integrity. Common types of constraints include primary key, foreign key, unique, not null, and check constraints.
Q-18 What is the difference between DELETE and TRUNCATE?
DELETE is a DML (Data Manipulation Language) command used to remove rows from a table based on a condition. TRUNCATE is a DDL (Data Definition Language) command used to remove all rows from a table, but it does not generate transaction logs and is faster than DELETE.
Q-19 What is a join?
A join is an operation that combines rows from two or more tables based on a related column between them. It is used to retrieve data from multiple tables in a single query.
Q-20 What are the types of joins in SQL?
The main types of joins in SQL are INNER JOIN, LEFT JOIN (or LEFT OUTER JOIN), RIGHT JOIN (or RIGHT OUTER JOIN), and FULL JOIN (or FULL OUTER JOIN).
Q-21 What is a subquery?
A subquery is a query nested within another query (main query). It is used to retrieve data based on the results of another query and can be used in SELECT, INSERT, UPDATE, and DELETE statements.
Q-22 What is the difference between CHAR and VARCHAR data types?
CHAR is a fixed-length character data type that stores a specific number of characters, padding any unused space with trailing blanks. VARCHAR is a variable-length character data type that stores a variable number of characters without padding.
Q-23 What is the difference between UNION and UNION ALL?
UNION is used to combine the results of two or more SELECT statements into a single result set, removing duplicate rows. UNION ALL also combines results but retains all rows, including duplicates.
Q-24 What is the difference between a clustered and a non-clustered index?
A clustered index determines the physical order of data in a table and is created on the primary key by default. A non-clustered index does not affect the physical order of data and is stored separately from the table data.
Q-25 What is a deadlock?
A deadlock occurs when two or more transactions are waiting indefinitely for resources locked by each other, preventing any of them from progressing. It can lead to a system-wide halt and requires intervention to resolve.
Q-26 What is a database backup?
A database backup is a copy of the database's data and schema that is taken periodically to safeguard against data loss due to hardware failure, corruption, or accidental deletion.
Q-27 What is data integrity?
Data integrity refers to the accuracy, consistency, and reliability of data stored in a database. It ensures that data is valid, complete, and conforms to predefined rules and constraints.
Q-28 What is a query optimization?
Query optimization is the process of improving the performance of database queries by selecting the most efficient execution plan. It involves techniques such as index usage, join ordering, and data filtering to minimize resource consumption and query execution time.
Q-29 What is a NoSQL database?
NoSQL (Not Only SQL) databases are a type of database management system that diverge from the traditional relational database model. They are designed to handle large volumes of unstructured or semi-structured data and provide high scalability and performance.
Q-30 What is ACID in NoSQL databases?
In NoSQL databases, ACID properties are relaxed to some extent to achieve better scalability and performance. While many NoSQL databases support eventual consistency rather than immediate consistency, they still prioritize ensuring durability and availability of data.
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