-- 等值列在前，范围列在后
CREATE INDEX idx ON orders (status, created_at);
-- 适用于: WHERE status = 'pending' AND created_at > '2024-01-01'

CREATE INDEX idx ON users (email) INCLUDE (name, created_at);
-- 避免针对 email, name, created_at 的表查找 (Table scan)

CREATE INDEX idx ON users (email) WHERE deleted_at IS NULL;
-- 索引更小，仅包含活跃用户

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

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) 对比 OFFSET 的 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 *;

-- 查找没有索引的外键
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)
  );

-- 查找低速查询
SELECT query, mean_exec_time, calls
FROM pg_stat_statements
WHERE mean_exec_time > 100
ORDER BY mean_exec_time DESC;

-- 检查表膨胀 (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;

-- 连接限制（根据 RAM 调整）
ALTER SYSTEM SET max_connections = 100;
ALTER SYSTEM SET work_mem = '8MB';

-- 超时设置
ALTER SYSTEM SET idle_in_transaction_session_timeout = '30s';
ALTER SYSTEM SET statement_timeout = '30s';

-- 监控
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;

-- 安全默认值
REVOKE ALL ON SCHEMA public FROM public;

SELECT pg_reload_conf();