Postgres Patterns

-- 等值欄位優先，然後是範圍欄位CREATE INDEX idx ON orders (status, created_at);-- 適用於：WHERE status = 'pending' AND created_at > '2024-01-01'

CREATE INDEX idx ON users (email) INCLUDE (name, created_at);-- 避免 SELECT email, name, created_at 時的表格查詢

CREATE INDEX idx ON users (email) WHERE deleted_at IS NULL;-- 更小的索引，只包含活躍使用者

CREATE POLICY policy ON orders  USING ((SELECT auth.uid()) = user_id);  -- 用 SELECT 包裝！

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

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

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 *;

-- 找出未建索引的外鍵SELECT conrelid::regclass, a.attnameFROM pg_constraint cJOIN 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)  );
-- 找出慢查詢SELECT query, mean_exec_time, callsFROM pg_stat_statementsWHERE mean_exec_time > 100ORDER BY mean_exec_time DESC;
-- 檢查表格膨脹SELECT relname, n_dead_tup, last_vacuumFROM pg_stat_user_tablesWHERE n_dead_tup > 1000ORDER BY n_dead_tup DESC;

-- 連線限制（依 RAM 調整）ALTER SYSTEM SET max_connections = 100;ALTER SYSTEM SET work_mem = '8MB';
-- 逾時ALTER SYSTEM SET idle_in_transaction_session_timeout = '30s';ALTER SYSTEM SET statement_timeout = '30s';
-- 監控CREATE EXTENSION IF NOT EXISTS pg_stat_statements;
-- 安全預設值REVOKE ALL ON SCHEMA public FROM public;
SELECT pg_reload_conf();