Stripe normalizes customer data to 3NF: customers table (id, name, email), addresses table (id, customer_id, street, city), payment_methods table (id, customer_id, type, last4). Prevents update anomalies (change email once, not in 100 orders). Amazon normalizes product catalog: products table, categories table, product_categories junction table. Prevents deletion anomalies (delete product, keep category). Netflix normalizes viewing history: users table, movies table, viewing_history table (user_id, movie_id, watched_at). Prevents insertion anomalies (add movie without user watching it). Banks normalize account data to BCNF for regulatory compliance. E-commerce sites normalize to 3NF for inventory management.

Stripe: Normalize Customer Data to 3NF for Payment Processing

Stripe processes 1 billion payment transactions daily. Initial design stored customer data (name, email, address) in payments table. Problem: Customer data duplicated in millions of payment rows, update customer email requires updating millions of rows (update anomaly), cannot add customer without payment (insertion anomaly). Solution: Normalize to 3NF - separate customers, addresses, payment_methods, payments tables.

Stripe normalization: (1) customers table (id, name, email, created_at), (2) addresses table (id, customer_id, street, city, state, zip, country), (3) payment_methods table (id, customer_id, type, last4, exp_month, exp_year), (4) payments table (id, customer_id, payment_method_id, amount, status, created_at). Benefits: Update customer email once (not in millions of payments), add customer without payment, delete payment but keep customer data. Performance: Index customer_id in payments table for fast joins (< 10ms). Real-world: Stripe processes 30K+ payments per second with normalized schema.

-- Stripe normalized schema (simplified)

CREATE TABLE customers (

customer_id VARCHAR(50) PRIMARY KEY,

email VARCHAR(100) UNIQUE NOT NULL,

name VARCHAR(100),

created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP

);

CREATE TABLE addresses (

address_id VARCHAR(50) PRIMARY KEY,

customer_id VARCHAR(50) REFERENCES customers(customer_id) ON DELETE CASCADE,

street VARCHAR(200),

city VARCHAR(100),

state VARCHAR(50),

zip VARCHAR(20),

country VARCHAR(50),

is_default BOOLEAN DEFAULT false

);

CREATE TABLE payment_methods (

payment_method_id VARCHAR(50) PRIMARY KEY,

customer_id VARCHAR(50) REFERENCES customers(customer_id) ON DELETE CASCADE,

type VARCHAR(20), -- card, bank_account

last4 VARCHAR(4),

exp_month INT,

exp_year INT,

is_default BOOLEAN DEFAULT false

);

CREATE TABLE payments (

payment_id VARCHAR(50) PRIMARY KEY,

customer_id VARCHAR(50) REFERENCES customers(customer_id),

payment_method_id VARCHAR(50) REFERENCES payment_methods(payment_method_id),

amount DECIMAL(10,2) NOT NULL,

currency VARCHAR(3) DEFAULT 'USD',

status VARCHAR(20), -- succeeded, failed, pending

created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP

);

-- Indexes for performance