# Database

> PostgreSQL and MongoDB database design. Schema design, migrations, indexing, query optimization, RLS security policies. Don't use for application logic or API development.

- Skill: `neuron-one/database` (Agent Skill)
- Install (CLI): `npx skillmds@latest add neuron-one/database`
- Raw SKILL.md: https://api.skillmd.com/api/skills/neuron-one/database/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Security
- Author: neuron-one (https://skillmd.com/u/neuron-one)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/neuron-one/database

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# Database Development

## PostgreSQL
- Normalized schema (3NF minimum)
- UUID primary keys for distributed systems
- Created_at/updated_at timestamps on all tables
- Foreign key constraints with ON DELETE behavior
- Check constraints for data integrity

## Indexing
- B-tree for equality and range queries
- GIN for full-text search and JSONB
- Partial indexes for filtered queries
- Composite indexes: most selective column first
- EXPLAIN ANALYZE before and after

## Migrations
- Sequential numbered migrations
- Always include rollback (down migration)
- Never modify existing migration
- Test migration on copy of production data

## MongoDB
- Schema design by access patterns (not normalization)
- Embedding for 1:few relationships
- References for 1:many or many:many
- Compound indexes matching query patterns

## Query Optimization
- Avoid N+1: use JOINs or eager loading
- Pagination with cursor, not OFFSET
- Connection pooling (PgBouncer)
- Read replicas for heavy read workloads