postgres-patterns

# 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: `backend-patterns` - API and backend patterns - Skill: `database-migrations` - Safe schema changes ## When to Use This Skill - Writing SQL queries - Designing database schemas - Optimizing query performance - Implementing Row Level Security - Troubleshooting database issues - Setting up PostgreSQL configuration --- *Based on Supabase Agent Skills (credit: Supabase team) (MIT License)*