1. What is Database?

A database is a structured collection of organized and interconnected data. It efficiently stores, manages, and retrieves information. Data is organized into tables with rows and columns. Databases ensure data integrity, support concurrent access, and offer security and backup features. They are essential for storing and managing data for applications and decision-making processes. 

2. What is DBMS?

DBMS stands for Database Management System. It is software that enables the creation, management, and manipulation of databases. DBMS provides an interface for users to interact with databases, allowing them to store, retrieve, and modify data. It handles tasks such as data organization, storage optimization, data security, and concurrency control. DBMS acts as an intermediary between users and the underlying database, providing efficient and reliable management of data.

3.  What is RDBMS? How is it different from DBMS?

RDBMS stands for Relational Database Management System. It is a type of DBMS that specifically manages relational databases. RDBMS uses a tabular structure, with tables consisting of rows and columns, to organize and store data. It enforces relationships between tables through keys, ensuring data integrity.

The main difference between RDBMS and DBMS is that RDBMS is built on the foundation of the relational model, which defines relationships between tables, while DBMS is a broader term that encompasses various types of database management systems, including non-relational ones. RDBMS offers features such as data normalization, which minimizes redundancy and ensures efficient data storage. It also supports the use of Structured Query Language (SQL) for querying and manipulating data. RDBMS provides a reliable and standardized approach for managing structured data, making it widely used in applications and systems that require a structured and organized data storage model.

4. What is SQL?

SQL stands for Structured Query Language. It is a standard programming language used for managing and manipulating relational databases. SQL allows users to create, modify, and retrieve data from databases. It provides a set of commands and syntax for performing tasks such as creating database tables, inserting data, updating records, and querying data. SQL is widely used across different database management systems and plays a crucial role in data manipulation, data definition, and data control within relational databases.

5. What is the difference between SQL and MySQL?

SQL and MySQL are related but distinct concepts:

SQL (Structured Query Language): SQL is a standardized programming language used for managing and manipulating relational databases. It provides a set of commands and syntax for tasks such as creating and modifying database structures, inserting, updating, and retrieving data, and performing various database operations. SQL is not tied to any specific database system and is supported by multiple database management systems, including MySQL.

MySQL: MySQL, on the other hand, is an open-source relational database management system (RDBMS) that implements the SQL language. It is one of the most popular and widely used RDBMS systems. MySQL provides a software platform that allows users to create, manage, and interact with relational databases using SQL queries. It offers features such as data storage, retrieval, and management, as well as user access control and security mechanisms.

In summary, SQL is a language used for interacting with databases, while MySQL is a specific RDBMS that utilizes SQL as its programming language. MySQL is just one of the many database management systems that support SQL as the query language.

6. What are Tables and Fields?

Tables: Tables are structures that hold related data in a tabular format, resembling spreadsheets. They consist of rows (records) and columns (fields) and provide a structured way to organize and store data in a database.

Fields: Fields, also known as columns or attributes, represent individual data elements within a table. Each field corresponds to a specific type of data and defines the characteristics of the stored data. Fields categorize and organize data within a table.

7. What are Constraints in SQL?

In SQL, constraints are rules or conditions applied to columns or tables to enforce data integrity and maintain consistency within a database. Here are the commonly used constraints in SQL:

• NOT NULL: Ensures that a column cannot contain NULL values.
• UNIQUE: Ensures that each value in a column is unique across the table.
• PRIMARY KEY: Enforces uniqueness and non-nullability of a column or a combination of columns. It uniquely identifies each record in a table. 
• FOREIGN KEY: Establishes a relationship between two tables, referencing a primary key in another table. It ensures referential integrity. 
• CHECK: Defines a condition that must be satisfied for the column values. It restricts the range of acceptable values. 
• DEFAULT: Specifies a default value for a column when no value is explicitly provided during an insert operation. 
• INDEX: Improves the performance of data retrieval by creating an index on one or more columns, allowing for faster data access.

8. What is a Primary Key?

In the context of databases, a primary key is a unique identifier for a record in a relational database table. It is a column or a combination of columns that uniquely identifies each row in the table. The primary key serves as a reference point to establish relationships between different tables in a database.

Here are some key characteristics of a primary key:

• Uniqueness: Each value in the primary key column(s) must be unique within the table. No two rows can have the same primary key value.
• Non-nullability: A primary key column cannot contain null values. It must have a value for every row in the table.
• Immutability: The primary key value should not change over time. If necessary, it should be updated with caution, considering the impact on other tables that reference it.
• Stability: The primary key value should remain relatively stable. Changing the primary key value frequently can lead to performance and integrity issues.
• Single-valued or minimal: A primary key can consist of a single column or a combination of multiple columns. In the latter case, the combination of values must be unique.

The primary key is crucial for maintaining data integrity and ensuring accurate data retrieval. It facilitates fast indexing and searching operations, as well as establishing relationships between tables through foreign keys.

9. What is a UNIQUE contraint?

A unique constraint is a rule or condition applied to a column or combination of columns in a database table that ensures that all values in that column or combination of columns are unique across the table. In other words, a unique constraint guarantees that no two rows in the table can have the same value(s) in the specified column(s).

Here are a few key points about unique constraints:

• Uniqueness: A unique constraint ensures that each value in the specified column(s) is unique within the table.
• Null values: By default, a unique constraint allows multiple rows to have a null value in the column(s) being constrained. However, most database systems provide an option to enforce uniqueness even for null values, known as a "unique constraint with nulls disallowed."
• Single column or combination: A unique constraint can be applied to a single column or a combination of columns. When applied to multiple columns, the combination of values must be unique.
• Automatic index creation: In many database systems, when a unique constraint is defined on a column or columns, an index is automatically created to improve the performance of unique value checks.

Unique constraints are useful for maintaining data integrity and preventing duplicates in a table. They are often applied to columns that should have distinct values, such as primary key columns or columns that should be unique based on the application's requirements.