claudekit/.claude/skills/databases/postgresql/SKILL.md

PostgreSQL

Description

PostgreSQL database patterns including queries, indexing, and optimization.

When to Use

• PostgreSQL database operations
• SQL query optimization
• Schema design

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Core Patterns

Basic Queries

-- Select with filtering
SELECT id, name, email
FROM users
WHERE active = true
ORDER BY created_at DESC
LIMIT 20 OFFSET 0;

-- Join
SELECT u.*, COUNT(p.id) as post_count
FROM users u
LEFT JOIN posts p ON p.user_id = u.id
GROUP BY u.id;

Indexes

-- Single column index
CREATE INDEX idx_users_email ON users(email);

-- Composite index
CREATE INDEX idx_posts_user_date ON posts(user_id, created_at DESC);

-- Partial index
CREATE INDEX idx_active_users ON users(email) WHERE active = true;

Migrations

-- Add column with default
ALTER TABLE users ADD COLUMN role VARCHAR(50) DEFAULT 'user';

-- Add constraint
ALTER TABLE users ADD CONSTRAINT unique_email UNIQUE (email);

Best Practices

1. Use indexes for filtered/sorted columns
2. Use EXPLAIN ANALYZE for slow queries
3. Avoid SELECT * in production
4. Use transactions for multiple operations
5. Use connection pooling

Common Pitfalls

• N+1 queries: Use JOINs or batch loading
• Missing indexes: Add indexes for WHERE/ORDER BY
• Large transactions: Keep transactions short