Database Schema Designer

Design production-ready database schemas with best practices built-in.

---

Quick Start

Just describe your data model:

design a schema for an e-commerce platform with users, products, orders

You'll get a complete SQL schema like:

CREATE TABLE users (
  id BIGINT AUTO_INCREMENT PRIMARY KEY,
  email VARCHAR(255) UNIQUE NOT NULL,
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

CREATE TABLE orders (
  id BIGINT AUTO_INCREMENT PRIMARY KEY,
  user_id BIGINT NOT NULL REFERENCES users(id),
  total DECIMAL(10,2) NOT NULL,
  INDEX idx_orders_user (user_id)
);

What to include in your request:

• Entities (users, products, orders)
• Key relationships (users have orders, orders have items)
• Scale hints (high-traffic, millions of records)
• Database preference (SQL/NoSQL) - defaults to SQL if not specified

---

Triggers

Trigger	Example
design schema	"design a schema for user authentication"
database design	"database design for multi-tenant SaaS"
create tables	"create tables for a blog system"
schema for	"schema for inventory management"
model data	"model data for real-time analytics"
I need a database	"I need a database for tracking orders"
design NoSQL	"design NoSQL schema for product catalog"

---

Key Terms

Term	Definition
Normalization	Organizing data to reduce redundancy (1NF → 2NF → 3NF)
3NF	Third Normal Form - no transitive dependencies between columns
OLTP	Online Transaction Processing - write-heavy, needs normalization
OLAP	Online Analytical Processing - read-heavy, benefits from denormalization
Foreign Key (FK)	Column that references another table's primary key
Index	Data structure that speeds up queries (at cost of slower writes)
Access Pattern	How your app reads/writes data (queries, joins, filters)
Denormalization	Intentionally duplicating data to speed up reads

---

Quick Reference

Task	Approach	Key Consideration
New schema	Normalize to 3NF first	Domain modeling over UI
SQL vs NoSQL	Access patterns decide	Read/write ratio matters
Primary keys	INT or UUID	UUID for distributed systems
Foreign keys	Always constrain	ON DELETE strategy critical
Indexes	FKs + WHERE columns	Column order matters
Migrations	Always reversible	Backward compatible first

---

Process Overview

Your Data Requirements
    |
    v
+-----------------------------------------------------+
| Phase 1: ANALYSIS                                   |
| * Identify entities and relationships               |
| * Determine access patterns (read vs write heavy)   |
| * Choose SQL or NoSQL based on requirements         |
+-----------------------------------------------------+
    |
    v
+-----------------------------------------------------+
| Phase 2: DESIGN                                     |
| * Normalize to 3NF (SQL) or embed/reference (NoSQL) |
| * Define primary keys and foreign keys              |
| * Choose appropriate data types                     |
| * Add constraints (UNIQUE, CHECK, NOT NULL)         |
+-----------------------------------------------------+
    |
    v
+-----------------------------------------------------+
| Phase 3: OPTIMIZE                                   |
| * Plan indexing strategy                            |
| * Consider denormalization for read-heavy queries   |
| * Add timestamps (created_at, updated_at)           |
+-----------------------------------------------------+
    |
    v
+-----------------------------------------------------+
| Phase 4: MIGRATE                                    |
| * Generate migration scripts (up + down)            |
| * Ensure backward compatibility                     |
| * Plan zero-downtime deployment                     |
+-----------------------------------------------------+
    |
    v
Production-Ready Schema

---

Commands

Command	When to Use	Action
design schema for {domain}	Starting fresh	Full schema generation
normalize {table}	Fixing existing table	Apply normalization rules
add indexes for {table}	Performance issues	Generate index strategy
migration for {change}	Schema evolution	Create reversible migration
review schema	Code review	Audit existing schema

Workflow: Start with design schema → iterate with normalize → optimize with add indexes → evolve with migration

---

Core Principles

Principle	WHY	Implementation
Model the Domain	UI changes, domain doesn't	Entity names reflect business concepts
Data Integrity First	Corruption is costly to fix	Constraints at database level
Optimize for Access Pattern	Can't optimize for both	OLTP: normalized, OLAP: denormalized
Plan for Scale	Retrofitting is painful	Index strategy + partitioning plan

---

Anti-Patterns

Avoid	Why	Instead
VARCHAR(255) everywhere	Wastes storage, hides intent	Size appropriately per field
FLOAT for money	Rounding errors	DECIMAL(10,2)
Missing FK constraints	Orphaned data	Always define foreign keys
No indexes on FKs	Slow JOINs	Index every foreign key
Storing dates as strings	Can't compare/sort	DATE, TIMESTAMP types
SELECT * in queries	Fetches unnecessary data	Explicit column lists
Non-reversible migrations	Can't rollback	Always write DOWN migration
Adding NOT NULL without default	Breaks existing rows	Add nullable, backfill, then constrain

---

Verification Checklist

After designing a schema:

• Every table has a primary key
• All relationships have foreign key constraints
• ON DELETE strategy defined for each FK
• Indexes exist on all foreign keys
• Indexes exist on frequently queried columns
• Appropriate data types (DECIMAL for money, etc.)
• NOT NULL on required fields
• UNIQUE constraints where needed
• CHECK constraints for validation
• created_at and updated_at timestamps
• Migration scripts are reversible
• Tested on staging with production data

---

Normal Forms

Form	Rule	Violation Example
1NF	Atomic values, no repeating groups	product_ids = '1,2,3'
2NF	1NF + no partial dependencies	customer_name in order_items
3NF	2NF + no transitive dependencies	country derived from postal_code

1st Normal Form (1NF)

-- BAD: Multiple values in column
CREATE TABLE orders (
  id INT PRIMARY KEY,
  product_ids VARCHAR(255)  -- '101,102,103'
);

-- GOOD: Separate table for items
CREATE TABLE orders (
  id INT PRIMARY KEY,
  customer_id INT
);

CREATE TABLE order_items (
  id INT PRIMARY KEY,
  order_id INT REFERENCES orders(id),
  product_id INT
);

2nd Normal Form (2NF)

-- BAD: customer_name depends only on customer_id
CREATE TABLE order_items (
  order_id INT,
  product_id INT,
  customer_name VARCHAR(100),  -- Partial dependency!
  PRIMARY KEY (order_id, product_id)
);

-- GOOD: Customer data in separate table
CREATE TABLE customers (
  id INT PRIMARY KEY,
  name VARCHAR(100)
);

3rd Normal Form (3NF)

-- BAD: country depends on postal_code
CREATE TABLE customers (
  id INT PRIMARY KEY,
  postal_code VARCHAR(10),
  country VARCHAR(50)  -- Transitive dependency!
);

-- GOOD: Separate postal_codes table
CREATE TABLE postal_codes (
  code VARCHAR(10) PRIMARY KEY,
  country VARCHAR(50)
);

When to Denormalize

Scenario	Denormalization Strategy
Read-heavy reporting	Pre-calculated aggregates
Expensive JOINs	Cached derived columns
Analytics dashboards	Materialized views

-- Denormalized for performance
CREATE TABLE orders (
  id INT PRIMARY KEY,
  customer_id INT,
  total_amount DECIMAL(10,2),  -- Calculated
  item_count INT               -- Calculated
);

String Types

Type	Use Case	Example
CHAR(n)	Fixed length	State codes, ISO dates
VARCHAR(n)	Variable length	Names, emails
TEXT	Long content	Articles, descriptions

-- Good sizing
email VARCHAR(255)
phone VARCHAR(20)
country_code CHAR(2)

Numeric Types

Type	Range	Use Case
TINYINT	-128 to 127	Age, status codes
SMALLINT	-32K to 32K	Quantities
INT	-2.1B to 2.1B	IDs, counts
BIGINT	Very large	Large IDs, timestamps
DECIMAL(p,s)	Exact precision	Money
FLOAT/DOUBLE	Approximate	Scientific data

-- ALWAYS use DECIMAL for money
price DECIMAL(10, 2)  -- $99,999,999.99

-- NEVER use FLOAT for money
price FLOAT  -- Rounding errors!

Date/Time Types

DATE