postgres-patterns

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PostgreSQL database patterns for query optimization, schema design, indexing, and security. Based on Supabase best practices.

Design

What this skill does


# PostgreSQL Patterns

Quick reference for PostgreSQL best practices. For detailed guidance, use the `database-reviewer` agent.

## When to Activate

- Writing SQL queries or migrations
- Designing database schemas
- Troubleshooting slow queries
- Implementing Row Level Security
- Setting up connection pooling

## Quick Reference

### Index Cheat Sheet

| Query Pattern           | Index Type       | Example                                  |
| ----------------------- | ---------------- | ---------------------------------------- |
| `WHERE col = value`     | B-tree (default) | `CREATE INDEX idx ON t (col)`            |
| `WHERE col > value`     | B-tree           | `CREATE INDEX idx ON t (col)`            |
| `WHERE a = x AND b > y` | Composite        | `CREATE INDEX idx ON t (a, b)`           |
| `WHERE jsonb @> '{}'`   | GIN              | `CREATE INDEX idx ON t USING gin (col)`  |
| `WHERE tsv @@ query`    | GIN              | `CREATE INDEX idx ON t USING gin (col)`  |
| Time-series ranges      | BRIN             | `CREATE INDEX idx ON t USING brin (col)` |

### Data Type Quick Reference

| Use Case   | Correct Type    | Avoid              |
| ---------- | --------------- | ------------------ |
| IDs        | `bigint`        | `int`, random UUID |
| Strings    | `text`          | `varchar(255)`     |
| Timestamps | `timestamptz`   | `timestamp`        |
| Money      | `numeric(10,2)` | `float`            |
| Flags      | `boolean`       | `varchar`, `int`   |

### Common Patterns

**Composite Index Order:**

```sql
-- Equality columns first, then range columns
CREATE INDEX idx ON orders (status, created_at);
-- Works for: WHERE status = 'pending' AND created_at > '2024-01-01'
```

**Covering Index:**

```sql
CREATE INDEX idx ON users (email) INCLUDE (name, created_at);
-- Avoids table lookup for SELECT email, name, created_at
```

**Partial Index:**

```sql
CREATE INDEX idx ON users (email) WHERE deleted_at IS NULL;
-- Smaller index, only includes active users
```

**RLS Policy (Optimized):**

```sql
CREATE POLICY policy ON orders
  USING ((SELECT auth.uid()) = user_id);  -- Wrap in SELECT!
```

**UPSERT:**

```sql
INSERT INTO settings (user_id, key, value)
VALUES (123, 'theme', 'dark')
ON CONFLICT (user_id, key)
DO UPDATE SET value = EXCLUDED.value;
```

**Cursor Pagination:**

```sql
SELECT * FROM products WHERE id > $last_id ORDER BY id LIMIT 20;
-- O(1) vs OFFSET which is O(n)
```

**Queue Processing:**

```sql
UPDATE jobs SET status = 'processing'
WHERE id = (
  SELECT id FROM jobs WHERE status = 'pending'
  ORDER BY created_at LIMIT 1
  FOR UPDATE SKIP LOCKED
) RETURNING *;
```

### Anti-Pattern Detection

```sql
-- Find unindexed foreign keys
SELECT conrelid::regclass, a.attname
FROM pg_constraint c
JOIN pg_attribute a ON a.attrelid = c.conrelid AND a.attnum = ANY(c.conkey)
WHERE c.contype = 'f'
  AND NOT EXISTS (
    SELECT 1 FROM pg_index i
    WHERE i.indrelid = c.conrelid AND a.attnum = ANY(i.indkey)
  );

-- Find slow queries
SELECT query, mean_exec_time, calls
FROM pg_stat_statements
WHERE mean_exec_time > 100
ORDER BY mean_exec_time DESC;

-- Check table bloat
SELECT relname, n_dead_tup, last_vacuum
FROM pg_stat_user_tables
WHERE n_dead_tup > 1000
ORDER BY n_dead_tup DESC;
```

### Configuration Template

```sql
-- Connection limits (adjust for RAM)
ALTER SYSTEM SET max_connections = 100;
ALTER SYSTEM SET work_mem = '8MB';

-- Timeouts
ALTER SYSTEM SET idle_in_transaction_session_timeout = '30s';
ALTER SYSTEM SET statement_timeout = '30s';

-- Monitoring
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;

-- Security defaults
REVOKE ALL ON SCHEMA public FROM public;

SELECT pg_reload_conf();
```

## Related

- Agent: `postgre-database-reviewer` - Full database review workflow
- Skill: `backend-patterns` - API and backend patterns

---

_Based on [Supabase Agent Skills](https://github.com/supabase/agent-skills) (MIT License)_

Files: 1

Size: 4.0 KB

Complexity: 7/100

Category: Design

Source: https://github.com/joneqian/claude-skills-suite/tree/main/skills/postgres-patterns

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