Database Schema Design

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name: database-schema-design
description: "Document or design a database schema with entity relationships, table definitions, constraints, indexes, and access patterns. Use when asked to design a database, document an existing schema, model entities and relationships, define table structures, plan an index strategy, or produce a data model for review. Produces a structured schema document covering an ER diagram, table DDL definitions, index strategy, access pattern analysis, normalization decisions, and migration notes."
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# Database Schema Design Skill

Produce a complete database schema design document for a given domain. A schema document is not just a list of tables — it is a record of decisions: what was modelled, how entities relate, which queries the schema is optimised for, and what trade-offs were made.

A good schema design document lets an engineer understand the data model, query it correctly, extend it safely, and write migrations without breaking things.

## Required Inputs

Ask for these if not already provided:
- **Domain description** — what the system does; what business objects are being modelled
- **Entities and relationships** — the main things in the domain and how they relate (e.g. "a User has many Orders; an Order has many OrderItems; an OrderItem references a Product")
- **Expected query patterns** — the most important read and write queries (e.g. "fetch all orders for a user, sorted by date"; "look up a product by SKU")
- **Database engine** — PostgreSQL, MySQL, SQLite, CockroachDB, etc. — this affects DDL syntax and available types
- **Expected data volume** — approximate row counts, growth rate, and any partitioning needs
- **Constraints** — any existing conventions, naming standards, or migration constraints to respect

## Output Format

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