# SQL

> SQL and database best practices including query optimization, indexing, and schema design. Use when this capability is needed.

- Skill: `tomevault-io/sql-2` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/sql-2`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/sql-2/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Data & Analytics
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/sql-2

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# SQL Best Practices

## Query Writing
- Use parameterized queries (prevent SQL injection)
- Select only needed columns (avoid SELECT *)
- Use appropriate JOINs
- Add WHERE clauses to limit results
- Use EXPLAIN to analyze queries

## Indexing
- Index columns used in WHERE/JOIN/ORDER BY
- Use composite indexes for multi-column queries
- Don't over-index (slows writes)
- Consider covering indexes
- Monitor index usage

## Schema Design
- Use appropriate data types
- Add constraints (NOT NULL, UNIQUE, FK)
- Normalize to 3NF, denormalize for performance
- Use UUIDs for distributed systems
- Add created_at/updated_at columns

## Transactions
- Keep transactions short
- Use appropriate isolation levels
- Handle deadlocks gracefully
- Use optimistic locking when appropriate

## Migrations
- Make migrations reversible
- Test migrations on copy of prod data
- Use small, focused migrations
- Never modify existing migrations
- Back up before migrating

## Performance
- Use connection pooling
- Implement pagination
- Cache frequent queries
- Use read replicas
- Monitor slow queries

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> Source: [kprsnt2/MyLocalCLI](https://github.com/kprsnt2/MyLocalCLI) — distributed by [TomeVault](https://tomevault.io).
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