2-1 Introduction to Relational Databases

Key Concepts

• Tables
• Rows and Columns
• Primary Keys
• Foreign Keys
• Relationships

Tables

Tables are the fundamental building blocks of relational databases. Each table represents a specific entity or object, such as customers, products, or orders. Tables are composed of rows and columns, where each row represents a single record, and each column represents an attribute of that record.

Example: A table named "Customers" might have columns like "CustomerID," "Name," "Address," and "PhoneNumber." Each row in this table represents a unique customer.

Rows and Columns

Rows, also known as tuples or records, represent individual entries in a table. Columns, also known as attributes or fields, represent the specific data points or characteristics of each entry. Together, rows and columns form a structured way to store and organize data.

Example: In the "Customers" table, a row might contain the data for a single customer, such as "1, John Doe, 123 Main St, 555-1234." The columns would be "CustomerID," "Name," "Address," and "PhoneNumber."

Primary Keys

Primary Keys are unique identifiers for each row in a table. They ensure that each record can be uniquely identified and accessed. A primary key can be a single column or a combination of columns.

Example: In the "Customers" table, "CustomerID" could be the primary key, ensuring that each customer has a unique identifier.

Foreign Keys

Foreign Keys are columns in one table that refer to the primary key in another table. They establish relationships between tables, allowing for data integrity and consistency across the database.

Example: In an "Orders" table, a foreign key like "CustomerID" would refer to the primary key "CustomerID" in the "Customers" table, linking each order to a specific customer.

Relationships

Relationships define how tables are connected through foreign keys. Common types of relationships include one-to-one, one-to-many, and many-to-many. These relationships help in organizing and querying data efficiently.

Example: A one-to-many relationship between "Customers" and "Orders" means that one customer can have many orders, but each order belongs to only one customer.

Conclusion

Understanding the key concepts of relational databases, such as tables, rows and columns, primary keys, foreign keys, and relationships, is essential for effective data management. These concepts provide a structured and efficient way to store, organize, and retrieve data, making relational databases a powerful tool for various applications.