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E-commerce Database Design

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Introduction

Designing a database for an e-commerce application involves understanding the various entities and their relationships within the system. This module will guide you through the process of creating a robust and scalable database design for an e-commerce platform.

Key Concepts

  1. Entities and Relationships: Identify the main entities (e.g., Users, Products, Orders) and their relationships.
  2. Normalization: Apply normalization principles to reduce redundancy and improve data integrity.
  3. Indexes: Use indexes to optimize query performance.
  4. Constraints: Implement constraints to enforce data integrity.

Step-by-Step Guide

Step 1: Identify Entities

The first step is to identify the main entities in the e-commerce system. Common entities include:

  • Users: Customers who use the platform.
  • Products: Items available for purchase.
  • Orders: Transactions made by users.
  • Categories: Groupings of products.
  • Reviews: Feedback provided by users on products.

Step 2: Define Relationships

Next, define the relationships between these entities:

  • Users and Orders: One-to-Many (One user can place multiple orders).
  • Orders and Products: Many-to-Many (One order can contain multiple products, and one product can be in multiple orders).
  • Products and Categories: Many-to-Many (One product can belong to multiple categories, and one category can contain multiple products).
  • Users and Reviews: One-to-Many (One user can write multiple reviews).
  • Products and Reviews: One-to-Many (One product can have multiple reviews).

Step 3: Create Tables

Based on the identified entities and relationships, create the necessary tables.

Users Table

CREATE TABLE Users (
    user_id SERIAL PRIMARY KEY,
    username VARCHAR(50) NOT NULL UNIQUE,
    email VARCHAR(100) NOT NULL UNIQUE,
    password VARCHAR(255) NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

Products Table

CREATE TABLE Products (
    product_id SERIAL PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    description TEXT,
    price DECIMAL(10, 2) NOT NULL,
    stock INT NOT NULL,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

Orders Table

CREATE TABLE Orders (
    order_id SERIAL PRIMARY KEY,
    user_id INT NOT NULL,
    order_date TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    total DECIMAL(10, 2) NOT NULL,
    FOREIGN KEY (user_id) REFERENCES Users(user_id)
);

OrderItems Table (to handle Many-to-Many relationship between Orders and Products)

CREATE TABLE OrderItems (
    order_id INT NOT NULL,
    product_id INT NOT NULL,
    quantity INT NOT NULL,
    price DECIMAL(10, 2) NOT NULL,
    PRIMARY KEY (order_id, product_id),
    FOREIGN KEY (order_id) REFERENCES Orders(order_id),
    FOREIGN KEY (product_id) REFERENCES Products(product_id)
);

Categories Table

CREATE TABLE Categories (
    category_id SERIAL PRIMARY KEY,
    name VARCHAR(50) NOT NULL UNIQUE
);

ProductCategories Table (to handle Many-to-Many relationship between Products and Categories)

CREATE TABLE ProductCategories (
    product_id INT NOT NULL,
    category_id INT NOT NULL,
    PRIMARY KEY (product_id, category_id),
    FOREIGN KEY (product_id) REFERENCES Products(product_id),
    FOREIGN KEY (category_id) REFERENCES Categories(category_id)
);

Reviews Table

CREATE TABLE Reviews (
    review_id SERIAL PRIMARY KEY,
    user_id INT NOT NULL,
    product_id INT NOT NULL,
    rating INT CHECK (rating >= 1 AND rating <= 5),
    comment TEXT,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES Users(user_id),
    FOREIGN KEY (product_id) REFERENCES Products(product_id)
);

Step 4: Indexes and Constraints

Indexes

Indexes can significantly improve the performance of your queries. Here are some examples:

CREATE INDEX idx_users_email ON Users(email);
CREATE INDEX idx_products_name ON Products(name);
CREATE INDEX idx_orders_user_id ON Orders(user_id);

Constraints

Constraints ensure data integrity. Here are some examples:

  • Unique Constraints: Ensure that certain columns have unique values.
  • Foreign Key Constraints: Ensure that a value in one table corresponds to a valid value in another table.

Step 5: Sample Data Insertion

To test the database design, insert some sample data.

-- Insert Users
INSERT INTO Users (username, email, password) VALUES
('john_doe', '[email protected]', 'password123'),
('jane_doe', '[email protected]', 'password456');

-- Insert Categories
INSERT INTO Categories (name) VALUES
('Electronics'),
('Books'),
('Clothing');

-- Insert Products
INSERT INTO Products (name, description, price, stock) VALUES
('Laptop', 'A high-performance laptop', 999.99, 10),
('Smartphone', 'A latest model smartphone', 699.99, 20),
('T-shirt', 'A comfortable cotton t-shirt', 19.99, 50);

-- Insert Orders
INSERT INTO Orders (user_id, total) VALUES
(1, 1019.98),
(2, 719.98);

-- Insert OrderItems
INSERT INTO OrderItems (order_id, product_id, quantity, price) VALUES
(1, 1, 1, 999.99),
(1, 3, 1, 19.99),
(2, 2, 1, 699.99);

-- Insert Reviews
INSERT INTO Reviews (user_id, product_id, rating, comment) VALUES
(1, 1, 5, 'Excellent laptop!'),
(2, 2, 4, 'Great smartphone, but a bit expensive.');

Practical Exercise

Exercise

  1. Create a new table: Add a ShippingAddresses table to store users' shipping addresses.
  2. Insert sample data: Insert sample data into the ShippingAddresses table.
  3. Query data: Write a query to retrieve all orders along with the user's shipping address.

Solution

Create ShippingAddresses Table

CREATE TABLE ShippingAddresses (
    address_id SERIAL PRIMARY KEY,
    user_id INT NOT NULL,
    address_line1 VARCHAR(255) NOT NULL,
    address_line2 VARCHAR(255),
    city VARCHAR(100) NOT NULL,
    state VARCHAR(100) NOT NULL,
    postal_code VARCHAR(20) NOT NULL,
    country VARCHAR(100) NOT NULL,
    FOREIGN KEY (user_id) REFERENCES Users(user_id)
);

Insert Sample Data

INSERT INTO ShippingAddresses (user_id, address_line1, address_line2, city, state, postal_code, country) VALUES
(1, '123 Main St', 'Apt 4B', 'New York', 'NY', '10001', 'USA'),
(2, '456 Elm St', NULL, 'Los Angeles', 'CA', '90001', 'USA');

Query Data

SELECT 
    Orders.order_id,
    Orders.order_date,
    Orders.total,
    Users.username,
    ShippingAddresses.address_line1,
    ShippingAddresses.address_line2,
    ShippingAddresses.city,
    ShippingAddresses.state,
    ShippingAddresses.postal_code,
    ShippingAddresses.country
FROM 
    Orders
JOIN 
    Users ON Orders.user_id = Users.user_id
JOIN 
    ShippingAddresses ON Users.user_id = ShippingAddresses.user_id;

Conclusion

In this module, we covered the essential steps to design a database for an e-commerce application. We identified key entities, defined their relationships, created tables, and implemented indexes and constraints. Additionally, we provided practical exercises to reinforce the concepts learned. This foundation will help you build a scalable and efficient e-commerce database.

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