claudegoodies
Skill

sql-optimization-patterns

From wshobson

Master SQL query optimization, indexing strategies, and EXPLAIN analysis to dramatically improve database performance and eliminate slow queries. Use when debugging slow queries, designing database schemas, or optimizing application performance.

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wshobson/agents
Status
Actively maintained
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Source file
plugins/developer-essentials/skills/sql-optimization-patterns/SKILL.md

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The instructions Claude Code reads when this skill runs.

# SQL Optimization Patterns

Transform slow database queries into lightning-fast operations through systematic optimization, proper indexing, and query plan analysis.

## When to Use This Skill

- Debugging slow-running queries
- Designing performant database schemas
- Optimizing application response times
- Reducing database load and costs
- Improving scalability for growing datasets
- Analyzing EXPLAIN query plans
- Implementing efficient indexes
- Resolving N+1 query problems

## Core Concepts

### 1. Query Execution Plans (EXPLAIN)

Understanding EXPLAIN output is fundamental to optimization.

**PostgreSQL EXPLAIN:**

```sql
-- Basic explain
EXPLAIN SELECT * FROM users WHERE email = '[email protected]';

-- With actual execution stats
EXPLAIN ANALYZE
SELECT * FROM users WHERE email = '[email protected]';

-- Verbose output with more details
EXPLAIN (ANALYZE, BUFFERS, VERBOSE)
SELECT u.*, o.order_total
FROM users u
JOIN orders o ON u.id = o.user_id
WHERE u.created_at > NOW() - INTERVAL '30 days';
```

**Key Metrics to Watch:**

- **Seq Scan**: Full table scan (usually slow for large tables)
- **Index Scan**: Using index (good)
- **Index Only Scan**: Using index without touching table (best)
- **Nested Loop**: Join method (okay for small datasets)
- **Hash Join**: Join method (good for larger datasets)
- **Merge Join**: Join method (good for sorted data)
- **Cost**: Estimated q
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