Database/DBMS & Types of Keys in Database Video Lecture | SSC CGL Tier 2 - Study Material, Online Tests, Previous Year

Ans. A database is an organized collection of data that is stored and accessed electronically. It is designed to efficiently manage and retrieve large amounts of information. A Database Management System (DBMS) is software that provides an interface between users and the database. It allows users to interact with the database, perform queries, and manage the data.

Ans. In a database, keys are used to uniquely identify records in a table. There are several types of keys: - Primary Key: A primary key is a column or a combination of columns that uniquely identifies each row in a table. It cannot have duplicate or null values. - Foreign Key: A foreign key is a column or a combination of columns that refers to the primary key of another table. It establishes a relationship between two tables. - Candidate Key: A candidate key is a column or a combination of columns that can be chosen as the primary key. It satisfies the uniqueness and irreducibility constraints. - Unique Key: A unique key is a column or a combination of columns that ensures the values in the key are unique. Unlike the primary key, it can have null values. - Composite Key: A composite key is a combination of two or more columns that collectively act as a primary key. It offers a higher level of uniqueness than a single column key.

Ans. The main difference between a primary key and a foreign key is their purpose and usage: - Primary Key: A primary key is used to uniquely identify each row in a table. It ensures that the values in the key are unique and cannot be null. Each table can have only one primary key. - Foreign Key: A foreign key is used to establish a relationship between two tables. It refers to the primary key of another table, creating a link between them. It helps maintain referential integrity and enforces data integrity rules.

Ans. Candidate keys play a crucial role in database design and normalization. They are used to identify unique rows in a table and help establish relationships between tables. The significance of candidate keys includes: - Uniqueness: Each candidate key ensures the uniqueness of rows in a table. This helps eliminate data redundancy and inconsistencies. - Primary Key Selection: Candidate keys are used to determine the primary key of a table. The primary key is chosen from the available candidate keys based on factors such as simplicity, stability, and uniqueness. - Referential Integrity: Candidate keys are used as foreign keys in other tables to establish relationships. They help maintain referential integrity by ensuring that referenced rows exist in the related table.

Ans. Yes, a table can have multiple foreign keys. This allows for the establishment of relationships with multiple tables. Each foreign key in a table refers to the primary key of a different table, creating connections between them. These relationships are essential for data integrity and allow for efficient querying and retrieval of related information.