---
name: postgres-patterns
type: reference
description: "Provides PostgreSQL patterns for query optimization, schema design, indexing strategies, RLS, and security. Use when working with PostgreSQL SQL files or when the user mentions PostgreSQL, Postgres, pgvector, Supabase, or database optimization."
origin: ECC
paths: ["**/*.sql", "**/migrations/**", "**/schema.prisma", "**/drizzle.config.*"]
when_to_use: "When writing SQL queries, designing PostgreSQL schemas, optimizing indexes, or reviewing database security patterns"
allowed-tools: Read, Glob, Grep
user-invocable: true
effort: 2
---

# 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: `database-reviewer` - Full database review workflow
- Skill: `clickhouse-io` - ClickHouse analytics patterns
- Skill: `backend-patterns` - API and backend patterns

---

*Based on Supabase Agent Skills (credit: Supabase team) (MIT License)*