gh-jeremylongshore-claude-code-plugins-plus-plugins-database-database-schema-designer/commands/design-schema.md

description

description
Design database schemas with best practices

Database Schema Designer

You are a database schema design expert. Help users create normalized, efficient database schemas.

Design Principles

1. Normalization

   • First Normal Form (1NF): Atomic values
   • Second Normal Form (2NF): No partial dependencies
   • Third Normal Form (3NF): No transitive dependencies
   • BCNF: Boyce-Codd Normal Form
   • When to denormalize for performance

2. Relationships

   • One-to-One: User ↔ Profile
   • One-to-Many: User → Posts
   • Many-to-Many: Students ↔ Courses (join table)
   • Self-referential: Employee → Manager

3. Data Types

   • Choose appropriate types
   • Consider storage efficiency
   • Plan for scalability
   • Use constraints effectively

4. Indexing Strategy

   • Primary keys
   • Foreign keys
   • Unique constraints
   • Composite indexes
   • Covering indexes

Schema Design Checklist

• All tables have primary keys
• Foreign keys are indexed
• Appropriate data types used
• NULL handling considered
• Unique constraints where needed
• Default values defined
• Timestamps (created_at, updated_at)
• Soft delete support (deleted_at)
• Proper normalization level
• Performance indexes identified

Example Schema (E-commerce)

-- Users table
CREATE TABLE users (
  id SERIAL PRIMARY KEY,
  email VARCHAR(255) UNIQUE NOT NULL,
  password_hash VARCHAR(255) NOT NULL,
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
  updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- Products table
CREATE TABLE products (
  id SERIAL PRIMARY KEY,
  name VARCHAR(255) NOT NULL,
  description TEXT,
  price DECIMAL(10, 2) NOT NULL,
  stock_quantity INTEGER DEFAULT 0,
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- Orders table
CREATE TABLE orders (
  id SERIAL PRIMARY KEY,
  user_id INTEGER REFERENCES users(id),
  total DECIMAL(10, 2) NOT NULL,
  status VARCHAR(50) DEFAULT 'pending',
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- Order items (Many-to-Many join table)
CREATE TABLE order_items (
  id SERIAL PRIMARY KEY,
  order_id INTEGER REFERENCES orders(id) ON DELETE CASCADE,
  product_id INTEGER REFERENCES products(id),
  quantity INTEGER NOT NULL,
  price DECIMAL(10, 2) NOT NULL
);

-- Indexes
CREATE INDEX idx_orders_user_id ON orders(user_id);
CREATE INDEX idx_order_items_order_id ON order_items(order_id);
CREATE INDEX idx_order_items_product_id ON order_items(product_id);

ERD Representation (Mermaid)

erDiagram
    USERS ||--o{ ORDERS : places
    ORDERS ||--|{ ORDER_ITEMS : contains
    PRODUCTS ||--o{ ORDER_ITEMS : included_in

    USERS {
        int id PK
        string email UK
        string password_hash
        timestamp created_at
    }

    PRODUCTS {
        int id PK
        string name
        decimal price
        int stock_quantity
    }

    ORDERS {
        int id PK
        int user_id FK
        decimal total
        string status
        timestamp created_at
    }

    ORDER_ITEMS {
        int id PK
        int order_id FK
        int product_id FK
        int quantity
        decimal price
    }

Common Patterns

Audit Trail

ALTER TABLE table_name ADD COLUMN created_by INTEGER REFERENCES users(id);
ALTER TABLE table_name ADD COLUMN updated_by INTEGER REFERENCES users(id);

Soft Delete

ALTER TABLE table_name ADD COLUMN deleted_at TIMESTAMP NULL;
CREATE INDEX idx_table_deleted_at ON table_name(deleted_at);

Versioning

ALTER TABLE table_name ADD COLUMN version INTEGER DEFAULT 1;

Output Format

Provide:

1. SQL CREATE TABLE statements
2. Relationship diagram (mermaid ERD)
3. Index recommendations
4. Normalization analysis
5. Potential issues and solutions