Database Schema Designer

Expert guidance on structuring data for scalability, integrity, and performance.

When to Use This Skill

• Designing a new database from scratch.
• Adding complex domains (e.g., "Add Social Features" or "Add Inventory Management").
• Deciding between SQL (Relational) vs NoSQL (Document/Graph).
• Troubleshooting architectural bottlenecks (Deadlocks, Hot partitions).
• Documenting data models with Entity-Relationship Diagrams (ERD).

Core Concepts

1. Relational Modeling (SQL)

Normalization (The Rules)

• 1NF: Atomic values. (No comma-separated lists).
• 2NF: No partial dependencies. (All non-keys depend on the whole primary key).
• 3NF: No transitive dependencies. (Non-keys depend ONLY on the primary key, not other non-keys).

Denormalization (The Exception)

• Break rules intentionally for read performance (e.g., storing user_name on the comments table to avoid joins).
• Trade-off: Faster reads, complex updates (consistency).

2. NoSQL Modeling

Document (MongoDB)

• Embedding: "One-to-Few". (Embed addresses inside User).
• Referencing: "One-to-Many". (Reference OrderIDs inside User).
• Pattern: "Computed Pattern" (Read-heavy? Pre-calculate totals on write).

Key-Value (Redis/DynamoDB)

• Access Patterns First: You must know how you will query data before designing the schema.
• Single Table Design: Overloading keys (PK=User#123, SK=Order#456) to fetch related data in one request.

3. Scalability Patterns

• Sharding (Horizontal Scaling): Splitting data across multiple servers based on a "Shard Key" (e.g., UserID).
• Partitioning (PostgreSQL): Splitting huge tables by active range (e.g., orders_2024, orders_2025).

Workflow

1. Identify Entities: User, Product, Order.
2. Define Relationships:
   • One-to-One (User <-> Profile).
   • One-to-Many (User <-> Orders).
   • Many-to-Many (Students <-> Classes).
3. Choose Engine:
   • Structured, Strict Consistency? -> PostgreSQL.
   • Unstructured, High Write Throughput? -> MongoDB/Cassandra.
4. Draw ERD: Use Mermaid or textual description.

Example: E-Commerce Schema

erDiagram
    USER ||--o{ ORDER : places
    ORDER ||--|{ ORDER_ITEM : contains
    product ||--o{ ORDER_ITEM : included_in
    
    USER {
        uuid id PK
        string email
        jsonb preferences
    }
    
    ORDER {
        uuid id PK
        uuid user_id FK
        enum status
        timestamp created_at
    }

Resources

• PostgreSQL Database Design
• MongoDB Schema Design Patterns
• DynamoDB Design Guide