Database Designer

Convert a design request or existing schema into a structured, validated, production-ready artifact.

Activation

Use this skill when the user asks to:

• design or review a database schema (DDL, ERD, Prisma, JSON Schema)
• choose a database engine or decide SQL vs NoSQL

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• analyze normalization, constraints, naming or data types
• plan an indexing strategy or diagnose slow queries
• generate migration scripts with rollback
• interpret an EXPLAIN plan or diagnose N+1 patterns

Workflow

1. Classify the request: design | analyze | index | migrate | query | select-engine.
2. Load the relevant reference for that mode:
   • design / analyze → {baseDir}/references/database-design-reference.md
   • normalization questions → {baseDir}/references/normalization_guide.md
   • indexing / EXPLAIN → {baseDir}/references/index_strategy_patterns.md
   • engine selection → {baseDir}/references/database_selection_decision_tree.md

3. Run the appropriate script when the user provides a schema or queries:

   # Analyze schema for issues (normalization, constraints, naming, types)
   python {baseDir}/scripts/schema_analyzer.py --schema=<ddl_file>
   
   # Suggest index improvements for a query workload
   python {baseDir}/scripts/index_optimizer.py --schema=<ddl_file> --queries=<queries_file>
   
   # Generate up/down migration scripts
   python {baseDir}/scripts/migration_generator.py --before=<old_schema> --after=<new_schema>

4. Formalize the design: objects, relationships, constraints, normalization level, primary/foreign keys.
5. Emit the artifact: DDL, Mermaid ERD, Prisma schema, or JSON Schema — one format unless the user asks for multiple.
6. Declare trade-offs: note any denormalization choices, missing constraints, or engine-specific limitations.

Output Contract

• Open with the dominant design decision or issue found.
• Emit one primary artifact (DDL, ERD, or schema) per response.
• Annotate non-obvious choices (e.g. why a partial index, why a surrogate key).
• Declare Information Loss when the target format cannot express a constraint (e.g. CHECK logic in Prisma).
• Close with indexing recommendations and next migration step if applicable.

Key Rules

• Default to PostgreSQL unless the user specifies another engine or the decision tree points elsewhere.
• Default to 3NF for new schemas; document any intentional deviation and the reason.
• Every generated migration must include a down script.
• For destructive changes (DROP COLUMN with data), always recommend a logical backup first.
• Do not generate application-layer connection pool code unless explicitly asked — reference the patterns instead.

Guardrails

• Do not skip normalization analysis when designing from scratch.
• Do not recommend over-indexing — flag indexes that may hurt write throughput.
• Flag N+1 patterns but do not generate ORM-specific code unless the user's stack is known.
• Stay within schema, index, migration and query scope; for large-scale cross-engine migrations refer to migration-architect.

Self Check

Before emitting any artifact, verify:

• all foreign keys are declared;
• primary key strategy is explicit (surrogate vs natural);
• normalization level is stated and intentional deviations justified;
• migration script has a down counterpart;
• no inline example code duplicates what a reference file already covers.