Transactions

• Definition: A transaction is a sequence of database operations performed as a single logical unit of work. It is designed to ensure the consistency and integrity of a database.
• Key Properties: Transactions follow ACID properties:
• Atomicity: All operations succeed or none are executed.
• Consistency: The database remains consistent before and after the transaction.
• Isolation: Transactions don’t interfere with each other.
• Durability: Changes remain permanent after the transaction is complete.

2. Normalization

• Definition: Normalization is the process of organizing a database to reduce redundancy and improve data integrity.
• Purpose: It breaks data into smaller tables and defines relationships between them.
• Normal Forms: Common forms include:
• 1NF (First Normal Form): Eliminate duplicate columns.
• 2NF (Second Normal Form): Remove partial dependencies.
• 3NF (Third Normal Form): Remove transitive dependencies.

3. ER Models

• Definition: An Entity-Relationship (ER) Model is a graphical representation of entities (objects) and their relationships in a database.
• Components:
• Entity: Represents objects or concepts (e.g., "Student").
• Attributes: Describe properties of an entity (e.g., "Name," "Age").
• Relationships: Define associations between entities (e.g., "Student enrolls in Courses").

4. Tiers

• Definition: Tiers refer to the architectural design of a database system, commonly divided into layers.
• Types:
• 1-Tier Architecture: Database resides on a single machine.
• 2-Tier Architecture: Client communicates directly with the database server.
• 3-Tier Architecture: Client, application server (handles logic), and database server are separate.

5. Schema

• Definition: A schema defines the structure of a database, including tables, fields, relationships, views, indexes, and constraints.
• Types:
• Physical Schema: Defines how data is stored.
• Logical Schema: Defines the structure at the logical level (e.g., tables, columns).
• View Schema: Defines user-specific views of the data.

6. ER Diagram

• Definition: An ER Diagram is a visual representation of an ER model.
• Purpose: Helps in designing and understanding the database structure.
• Symbols:
• Rectangle: Entity.
• Oval: Attribute.
• Diamond: Relationship.

7. SQL Join

• Definition: A JOIN in SQL is used to combine rows from two or more tables based on a related column.
• Types:
• INNER JOIN: Returns matching rows in both tables.
• LEFT JOIN: Returns all rows from the left table and matching rows from the right.
• RIGHT JOIN: Returns all rows from the right table and matching rows from the left.
• FULL JOIN: Returns rows when there is a match in either table.

8. Database

• Definition: A database is an organized collection of data stored electronically in a structured manner for efficient retrieval, management, and updating.
• Examples:
• Relational databases (e.g., MySQL, PostgreSQL).
• NoSQL databases (e.g., MongoDB, Cassandra).
• Key Features:
• Data consistency.
• Support for queries using languages like SQL.
• Scalability and security.