Keys

 Keys

In relational databases, keys are attributes (or a combination of attributes) that help identify records in a table and create relationships between tables. They are important for maintaining data accuracy and avoiding duplicate records.

🔹 Primary Key

A primary key uniquely identifies each row in a table. It cannot contain duplicate or NULL values. Each table can have only one primary key.

🔹 Candidate Key

A candidate key is any attribute that can uniquely identify a record. A table may have multiple candidate keys, but only one is selected as the primary key.

🔹 Super Key

A super key is a set of one or more attributes that uniquely identify a record. It may include extra attributes along with a candidate key.

🔹 Foreign Key

A foreign key is an attribute in one table that refers to the primary key of another table. It helps maintain relationships and ensures referential integrity.

🔹 Composite Key

A composite key is formed by combining two or more attributes to uniquely identify a record.

Keys are essential in relational databases because they ensure uniqueness, maintain relationships, and support data integrity.


 Click here

Comments

Post a Comment

Popular posts from this blog

Views in Relational Databases

   Views in Relational Databases A View is a virtual table in a relational database. It is created using a SQL query and displays data from one or more tables. Unlike a regular table, a view does not store data physically; instead, it stores the query definition and retrieves data dynamically when accessed. Views are used to simplify complex queries, improve security, and present specific data to users without exposing the entire table. 🔹 Why Use Views? Security – Restrict access to specific columns or rows. Simplification – Hide complex joins and calculations. Data Abstraction – Show only required information to users. Consistency – Provide a standard way to access data. 🔹 Types of Views Simple View – Based on a single table without complex functions. Complex View – Based on multiple tables with joins, grouping, or functions. 🔹 Example (SQL Syntax) CREATE VIEW student_view AS SELECT name, department FROM student; click here to view
Read more

SQL

Introduction to SQL SQL (Structured Query Language) is a standard programming language used to manage and manipulate relational databases. It is used to create databases, insert data, retrieve data, update records, and delete data. SQL works with relational databases that store data in tables (rows and columns). It is easy to learn and widely used in industries such as banking, education, healthcare, and e-commerce.  Types of SQL Commands DDL (Data Definition Language) – CREATE, ALTER, DROP DML (Data Manipulation Language) – INSERT, UPDATE, DELETE DQL (Data Query Language) – SELECT DCL (Data Control Language) – GRANT, REVOKE TCL (Transaction Control Language) – COMMIT, ROLLBACK, SAVEPOINT SQL is essential for interacting with relational database systems efficiently.  Advanced SQL Features Advanced SQL features provide powerful capabilities for handling complex queries and database operations.  1️⃣ Joins Used to combine data from multiple tables (INNE...
Read more

EMBEDDED SQL

Embedded SQL Embedded SQL is a method of writing SQL statements inside a host programming language such as C, C++, or Java. It allows application programs to interact directly with a relational database. In Embedded SQL, SQL commands are written within the source code of the program and are processed by a special precompiler before compilation. The precompiler converts SQL statements into function calls that the programming language can understand. 🔹 Why Use Embedded SQL? To connect application programs with databases To retrieve and manipulate data directly from code To build database-driven applications 🔹 Key Features SQL statements are embedded inside programming code Uses host variables to pass values between the program and database Supports SELECT, INSERT, UPDATE, DELETE, and transaction control commands 🔹 Example (Conceptual Syntax in C) EXEC SQL SELECT name INTO : student_name FROM student WHERE roll_no = 1 ; Here, :student_name is a host varia...
Read more