**Course Title:** SQLite Mastery: Lightweight Database Management **Section Title:** Introduction to SQLite and Relational Databases **Topic:** Understanding the structure of relational databases **Introduction** In the previous topic, we explored what SQLite is and why it's a popular choice for database management. Now, let's dive deeper into the structure of relational databases, which is the foundation of SQLite and many other database systems. Understanding this structure will help you design and work with databases more effectively. **What is a Relational Database?** A relational database is a type of database that stores and provides access to data points that are related to each other. It's based on the relational model, which was first proposed by Edgar F. Codd in 1970 [1]. This model organizes data into one or more tables, with each table having rows and columns. **The Basic Components of a Relational Database** A relational database consists of the following basic components: 1. **Tables**: Also known as relations, tables are the fundamental data structures in a relational database. Each table represents a collection of related data, such as employees, customers, or orders. 2. **Columns**: Columns are the vertical elements of a table, and each column represents a field or attribute of the data, such as name, email, or phone number. 3. **Rows**: Rows are the horizontal elements of a table, and each row represents a single record or tuple of data. 4. **Primary Key**: A primary key is a unique identifier for each row in a table, ensuring that no two rows have the same primary key value. 5. **Foreign Key**: A foreign key is a field in a table that refers to the primary key of another table, establishing a relationship between the two tables. **Relationships Between Tables** Relationships between tables are a crucial aspect of relational databases. There are three main types of relationships: 1. **One-to-One (1:1)**: A one-to-one relationship exists when a single row in one table is related to only one row in another table. 2. **One-to-Many (1:N)**: A one-to-many relationship exists when a single row in one table is related to multiple rows in another table. 3. **Many-to-Many (M:N)**: A many-to-many relationship exists when multiple rows in one table are related to multiple rows in another table. **Example:** Suppose we have two tables, `orders` and `customers`. Each order is related to only one customer, and each customer can have multiple orders. This is an example of a one-to-many relationship. | orders | customers | | --- | --- | | id (PK) | id (PK) | | customer_id (FK) | name | | order_date | email | **SQL Commands for Creating and Managing Tables** To create and manage tables in a relational database, you use SQL (Structured Query Language) commands. Some common SQL commands include: * `CREATE TABLE`: Creates a new table with specified columns and data types. * `ALTER TABLE`: Modifies an existing table by adding, deleting, or renaming columns. * `DROP TABLE`: Deletes a table and all its data. For example, to create the `orders` table in SQLite, you would use the following SQL command: ```sql CREATE TABLE orders ( id INTEGER PRIMARY KEY, customer_id INTEGER NOT NULL, order_date DATE NOT NULL, FOREIGN KEY (customer_id) REFERENCES customers (id) ); ``` **Conclusion** In this topic, we explored the structure of relational databases, including tables, columns, rows, primary keys, and foreign keys. We also discussed relationships between tables and provided examples of one-to-one, one-to-many, and many-to-many relationships. Finally, we introduced SQL commands for creating and managing tables. **Practical Exercise** Try creating a simple database with two tables, `employees` and `departments`, and establish a one-to-many relationship between them. Use the SQLite command-line shell or a GUI tool like DB Browser for SQLite to create and manage your database. **Leave a comment or ask for help** If you have any questions or need help with the practical exercise, leave a comment below. We'll be happy to assist you. **References** [1] Codd, E. F. (1970). A relational model of data for large shared data banks. Communications of the ACM, 13(6), 377-387. [https://dl.acm.org/citation.cfm?id=362685](https://dl.acm.org/citation.cfm?id=362685) **What's next?** In the next topic, we'll cover setting up the SQLite development environment. We'll explore the SQLite command-line shell, GUI tools, and programming languages that support SQLite.