PostgreSQL 如果不存在就插入（存在则不插入
按 email 去重插入
INSERT INTO users (id, name, email) VALUES (1, '张三', 'test@qq.com') ON CONFLICT (email) DO NOTHING;
不存在插入，存在就更新
INSERT INTO users (id, name, age) VALUES (1, '张三', 20) ON CONFLICT (id) DO UPDATE SET name = EXCLUDED.name, age = EXCLUDED.age;
